JP7702072B2 - Tetracarboxylic dianhydride, carbonyl compound, polyimide precursor resin, and polyimide - Google Patents

Description

The present invention relates to tetracarboxylic dianhydrides, carbonyl compounds, polyimide precursor resins, and polyimides.

In general, tetracarboxylic dianhydrides are useful as raw materials for producing polyimide resins and epoxy curing agents. Among these tetracarboxylic dianhydrides, aromatic tetracarboxylic dianhydrides such as pyromellitic dianhydride have been mainly used as raw materials for polyimide resins used in the electronics field. As a polyimide obtained using such aromatic tetracarboxylic dianhydrides, for example, polyimide (trade name "Kapton") sold by DuPont Toray Co., Ltd., which has been an indispensable material for cutting-edge industries such as aerospace and aviation applications, is widely known. However, although polyimides obtained using conventional aromatic tetracarboxylic dianhydrides have excellent physical properties in terms of heat resistance, they are colored (yellow to brown) and cannot be used for optical applications requiring transparency.

Under these circumstances, research has been conducted into various aliphatic tetracarboxylic dianhydrides from the viewpoint of light transmittance in order to produce polyimides that can be used for optical applications. However, since such aliphatic tetracarboxylic dianhydrides have not always provided sufficient heat resistance when used to produce polyimides, research has been conducted in recent years into aliphatic tetracarboxylic dianhydrides that can produce polyimides with a high level of heat resistance. As such aliphatic tetracarboxylic acid dianhydrides, for example, WO 2018/147373 (Patent Document 1) discloses a tetracarboxylic acid dianhydride that is a compound consisting of a stereoisomer having an endo/exo type stereostructure of 5,5'-bi-2-norbornene-5,5',6,6'-tetracarboxylic acid-5,5',6,6'-dianhydride (hereinafter sometimes referred to as "BNBDA") and its enantiomer (stereoisomer having an exo/endo type stereoisomer), and a stereoisomer having an endo/endo type stereoisomer, in which the content ratio of the stereoisomer having an endo/endo type stereoisomer to the total amount of these stereoisomers is within a specific range.

International Publication No. 2018/147373

The tetracarboxylic dianhydride described in the above Patent Document 1 is an aliphatic tetracarboxylic dianhydride, but it is possible to produce polyimides having a high level of heat resistance. In the field of such aliphatic tetracarboxylic dianhydrides, there is a demand for the emergence of tetracarboxylic dianhydrides that can produce polyimides that can exhibit even higher levels of heat resistance depending on the application, etc.

The present invention has been made in consideration of the problems associated with the above-mentioned conventional techniques, and aims to provide a tetracarboxylic dianhydride that can be used as a raw material monomer for producing polyimides having a higher level of heat resistance and that can further improve polymerization reactivity when used as a raw material monomer for producing polyimides, a carbonyl compound that can be used to efficiently produce the tetracarboxylic dianhydride, a polyimide that can have a higher level of heat resistance, and a polyimide precursor resin that can be suitably used to produce the polyimide.

As a result of intensive research conducted by the present inventors to achieve the above object, it was discovered that when a polyimide is produced using a tetracarboxylic dianhydride comprising an acid dianhydride (A) having an exo/exo stereostructure represented by the following general formula (1) and/or at least one acid dianhydride (B) selected from the group consisting of a compound having an endo/exo stereostructure represented by the following general formula (2) and a compound having an exo/endo stereostructure which is its mirror image, and in which the content of the acid dianhydride (A) relative to the total amount of the acid dianhydrides (A) and (B) is 30 to 100 mol % in molar ratio, it is possible to obtain a polyimide having a higher level of heat resistance than conventional polyimides (e.g., polyimides as described in Patent Document 1), and it is also possible to further improve the polymerization reactivity during the production of the polyimide, thereby completing the present invention.

That is, the present invention provides the following aspects:

[1] General formula (1):

In formula (1), R ¹ each independently represents one selected from the group consisting of a hydrogen atom and a methyl group ;
^R2 and ^R3 each independently represent one selected from the group consisting of a hydrogen atom and a methyl group .
or a tetracarboxylic acid dianhydride comprising an acid dianhydride (A) having an exo/exo stereostructure represented by the following general formula (2):

[In formula (2), R ¹ , R ² and R ³ are the same as R ¹ , R ² and R ³ in formula (1), respectively.]
and a compound having an exo/endo stereostructure which is an enantiomer thereof, and
The tetracarboxylic acid dianhydride, wherein the content of the acid dianhydride (A) relative to the total amount of the acid dianhydrides (A) and (B) is 30 to 100 mol % in terms of molar ratio.

[2] General formula (3):

In formula (3), R ¹ each independently represents one selected from the group consisting of a hydrogen atom and a methyl group ;
^R2 and ^R3 each independently represent one selected from the group consisting of a hydrogen atom and a methyl group ;
Each R ⁴ independently represents one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, and an aralkyl group having 7 to 20 carbon atoms.
or a carbonyl compound comprising the carbonyl compound (A) having an exo/exo stereostructure represented by the following general formula (4):

[In formula (4), R ¹ , R ² , R ³ and R ⁴ are the same as R ¹ , R ² , R ³ and R ⁴ in formula (3) above, respectively.]
and a compound having an exo/endo stereostructure which is an enantiomer thereof, and
A carbonyl compound, wherein the content of the carbonyl compound (A) relative to the total amount of the carbonyl compounds (A) and (B) is 30 to 100 mol % in terms of molar ratio.

[3] General formula (5):

In formula (5), R ¹ each independently represents one selected from the group consisting of a hydrogen atom and a methyl group ;
^R2 and ^R3 each independently represent one selected from the group consisting of a hydrogen atom and a methyl group ;
R ⁵ represents an arylene group having 6 to 50 carbon atoms.
or a polyimide containing a repeating unit (A) having an exo/exo type stereostructure represented by the following general formula (6):

[In formula (6), R ¹ , R ² , R ³ and R ⁵ are the same as R ¹ , R ² , R ³ and R ⁵ in formula (5), respectively.]
and a structural unit having an exo/endo type stereostructure which is a mirror image thereof, and at least one repeating unit (B) selected from the group consisting of a structural unit having an endo/exo type stereostructure represented by the formula :
A polyimide in which the content of the repeating unit (A) relative to the total amount of the repeating units (A) and (B) is 30 to 100 mol % in terms of molar ratio.

[4] General formula (7):

In formula (7), R ¹ each independently represents one selected from the group consisting of a hydrogen atom and a methyl group ;
^R2 and ^R3 each independently represent one selected from the group consisting of a hydrogen atom and a methyl group ;
^R5 represents an arylene group having 6 to 50 carbon atoms;
Each Y ¹ independently represents one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, and an alkylsilyl group having 3 to 9 carbon atoms;
One of the bonds represented by *1 and *2 is bonded to the carbon atom a forming the norbornane ring, the other of the bonds represented by *1 and *2 is bonded to the carbon atom b forming the norbornane ring, one of the bonds represented by *3 and *4 is bonded to the carbon atom c forming the norbornane ring, and the other of the bonds represented by *3 and *4 is bonded to the carbon atom d forming the norbornane ring.]
or a polyimide precursor resin containing a repeating unit ( A') having an exo/exo type stereostructure represented by the following general formula (8):

[In formula (8), R ¹ , R ² , R ³ , R ⁵ , Y ¹ , a to d, and *1 to *4 are respectively defined as R ¹ , R ² , R ³ , R ⁵ , Y ¹ , a to d, and *1 to *4 in formula (7) above.]
and a structural unit having an exo/endo type stereostructure which is a mirror image thereof, and at least one repeating unit (B') selected from the group consisting of a structural unit having an endo/exo type stereostructure represented by the formula :
The polyimide precursor resin has a molar ratio of 30 to 100 mol % based on the total amount of the repeating units (A') and (B').

In addition, the expressions for the types of stereoisomers in this application are divided according to whether one bicyclo ring (norbornane ring) is bonded at the exo position or endo position of the other bicyclo ring (norbornane ring). For example, the above acid dianhydride (A) is expressed as an "exo/exo type" because one bicyclo ring is bonded to the exo position of the other bicyclo ring when viewed from both the left and right sides.

According to the present invention, it is possible to provide a tetracarboxylic dianhydride that can be used as a raw material monomer for producing polyimides having a higher level of heat resistance and that can further improve polymerization reactivity when used as a raw material monomer for producing polyimides, a carbonyl compound that can be used to efficiently produce the tetracarboxylic dianhydride, a polyimide that can have a higher level of heat resistance, and a polyimide precursor resin that can be suitably used to produce the polyimide.

The present invention will be described in detail below with reference to preferred embodiments thereof. In this specification, unless otherwise specified, the expression "X to Y" for numerical values X and Y means "X or more and Y or less." In such expressions, when a unit is added only to numerical value Y, the unit is also applied to numerical value X.

[Tetracarboxylic acid dianhydride]
The tetracarboxylic acid dianhydride of the present invention is characterized in that it comprises an acid dianhydride (A) having an exo/exo stereostructure represented by the above general formula (1) and/or at least one acid dianhydride (B) selected from the group consisting of a compound having an endo/exo stereostructure represented by the above general formula (2) and a compound having an exo/endo stereostructure that is an enantiomer thereof, and that the content of the acid dianhydride (A) relative to the total amount of the acid dianhydrides (A) and (B) is 30 to 100 mol % in molar ratio.

Note that the following formula (9):

[R ¹ , R ² and R ³ in formula (9) are the same as R ¹ , R ² and R ³ in formula (1) above, respectively.]
The tetracarboxylic dianhydride represented by the formula (1) includes, as stereoisomers, stereoisomer A (acid dianhydride (A)) having an exo/exo type stereostructure represented by the formula (1), stereoisomer B (acid dianhydride (B)) consisting of a compound having an endo/exo type stereostructure represented by the formula (2) and a compound having an exo/endo type stereostructure which is its mirror image, as well as stereoisomer C having an endo/endo type stereostructure. The tetracarboxylic dianhydride of the present invention is a compound (acid dianhydride) consisting of stereoisomer A and/or stereoisomer B among such stereoisomers A to C, in which the amount of stereoisomer A relative to the total amount of stereoisomer A and stereoisomer B is 30 to 100 mol % in molar ratio. Regarding the "stereoisomer B (acid dianhydride (B))" mentioned here, the stereoisomer having an endo/exo structure represented by the above general formula (2) (hereinafter, sometimes simply referred to as "stereoisomer B1") and/or its mirror image having an exo/endo structure (hereinafter, sometimes simply referred to as "stereoisomer B2") cannot be distinguished from each other by spectroscopy. Therefore, in the description of the stereoisomers mentioned above, the endo/exo structure and the exo/endo structure are considered to have equivalent isomeric structures, and the stereoisomer consisting of stereoisomer B1 and/or stereoisomer B2 is simply referred to as "stereoisomer B". In the present invention, the "compound having an endo/exo type stereostructure" which cannot be distinguished spectroscopically and its mirror image (enantiomer), the "compound having an exo/endo type stereostructure", are referred to as "acid dianhydride (B)".

R ¹ in the above general formula (1) each independently represents one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a hydroxyl group, and a nitro group, or two R ¹ in the above general formula (1) bonded to the same carbon atom may form a methylidene group together. The alkyl group that can be selected as R ¹ in the above general formula (1) is an alkyl group having 1 to 10 carbon atoms. If the number of carbon atoms exceeds 10, the heat resistance of the resulting polyimide decreases when used as a polyimide monomer. In addition, the ^number of carbon atoms of the alkyl group that can be selected as such R ¹ is preferably 1 to 6, more preferably 1 to 5, even more preferably 1 to 4, and particularly preferably 1 to 3, from the viewpoint of obtaining a higher level of heat resistance when producing a polyimide. In addition, the alkyl group that can be selected as such R ¹ may be linear or branched.

Among the multiple ^R1s in the general formula (1), two ^R1s bonded to the same carbon atom may be bonded together to form a methylidene group (= _CH2 ). That is, two ^R1s bonded to the same carbon atom in the general formula (1) may be bonded together to the carbon atom (the carbon atom to which two ^R1s are bonded among the carbon atoms forming the norbornane ring structure) via a double bond to form a methylidene group (methylene group).

The multiple R ^1s in the above general formula (1) are each preferably independently a hydrogen atom, a methyl group, an ethyl group, an n-propyl group, or an isopropyl group, and particularly preferably a hydrogen atom or a methyl group, from the viewpoints of obtaining a higher degree of heat resistance when producing a polyimide, of easy availability of raw materials, of easier purification, etc. Furthermore, the multiple R ^1s in such formula (1) may be the same or different, but are preferably the same from the viewpoint of ease of purification, etc.

R ² and R ³ in the above general formula (1) are each independently one selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 10 carbon atoms. If the number of carbon atoms of the alkyl group that can be selected as R ² and R ³ exceeds 10, when used as a polyimide monomer, the heat resistance of the resulting polyimide decreases. In addition, the alkyl group that can be selected as R ² and R ³ is preferably 1 to 6, more preferably 1 to 5, even more preferably 1 to 4, and particularly preferably 1 to 3, from the viewpoint of obtaining a higher degree of heat resistance when producing a polyimide. In addition, the alkyl group that can be selected as R ² and R ³ may be linear or branched.

From the viewpoints of obtaining a higher degree of heat resistance when the polyimide is produced, of easiness of obtaining raw materials, of easiness of purification, etc., R ² and R ³ in the above general formula (1) are each preferably independently a hydrogen atom, a methyl group, an ethyl group, an n-propyl group, or an isopropyl group, and are particularly preferably a hydrogen atom or a methyl group. Furthermore, R ² and R ³ in such formula (1) may be the same or different, but from the viewpoint of easiness of purification, etc., they are preferably the same.

In addition, it is particularly preferable that the plurality of R ¹ , R ² and R ³ in the general formula (1) are all hydrogen atoms. In this way, when the substituents represented by R ¹ , R ² and R ³ in the compound represented by the general formula (1) are all hydrogen atoms, the yield of the compound tends to be improved. In addition, when a polyimide is produced using the compound as a monomer, a higher degree of heat resistance tends to be obtained.

In addition, in the above general formula (2), R ¹ , R ² and R ³ have the same meanings as R ¹ , R ² and R ³ in the above general formula (1), and the preferred meanings thereof are also the same.

The acid dianhydride (B) may contain a compound having an endo/exo stereostructure and a compound having an exo/endo stereostructure, but the acid dianhydride (B) may contain either one of the compounds alone, or may contain both of these compounds.

The tetracarboxylic dianhydride of the present invention is composed of the above-mentioned acid dianhydride (A) and/or the above-mentioned acid dianhydride (B), and the content of the acid dianhydride (A) relative to the total amount of the acid dianhydrides (A) and (B) is 30 to 100 mol % in terms of molar ratio. By making the content of such acid dianhydride (A) equal to or higher than the lower limit, not only can a higher level of heat resistance be achieved when a polyimide is produced using this, but also, when the polyimide is used as a monomer for polymerization, polymerization reactivity can be further improved.

Furthermore, the content of the acid dianhydride (A) relative to the total amount of the acid dianhydrides (A) and (B) is more preferably 40 to 100 mol%, even more preferably 60 to 100 mol%, particularly preferably 80 to 100 mol%, and most preferably 90 to 100 mol%. When the content of the acid dianhydride (A) is within the above-mentioned preferred range, the heat resistance tends to be further improved when a polyimide is produced using the acid dianhydride (A).

The method for producing the tetracarboxylic dianhydride of the present invention will be described later.

[Carbonyl compounds]
The carbonyl compound of the present invention is characterized in that it comprises at least one carbonyl compound (B) selected from the group consisting of a carbonyl compound (A) having an exo/exo stereostructure represented by the above general formula (3) and/or a compound having an endo/exo stereostructure represented by the above general formula (4) and a compound having an exo/endo stereostructure which is its enantiomer, and the content of the carbonyl compound (A) relative to the total amount of the carbonyl compounds (A) and (B) is 30 to 100 mol % in molar ratio. Note that, regarding the carbonyl compound, the compound having an endo/exo stereostructure and its enantiomer (enantiomer), the compound having an exo/endo stereostructure, cannot be distinguished spectroscopically, and therefore these are referred to as "carbonyl compound (B)".

R ¹ , R ² and R ³ in the general formula (3) are the same as R ¹ , R ² and R ³ in the general formula (1), respectively, and the preferred ones are the same as R ¹ , R ² and R ³ in the general formula (1). Note that the multiple R ^1s in the general formula (3) may be the same or different, but are preferably the same from the viewpoint of ease of purification, etc. Furthermore, R ² and R ³ in the general formula (3) may be the same or different, but are preferably the same from the viewpoint of ease of purification, etc.

It is particularly preferred that the plurality of R ¹ , R ² and R ³ in the general formula (3) are all hydrogen atoms. In this way, when the substituents represented by R ¹ , R ² and R ³ in the compound represented by the general formula (3) are all hydrogen atoms, the yield of the compound tends to be improved. In addition, when an acid dianhydride is formed from the compound and a polyimide is produced using the obtained acid dianhydride as a monomer, a higher degree of heat resistance tends to be obtained.

Moreover, the alkyl group that can be selected as R ⁴ in the general formula (3) is an alkyl group having 1 to 10 carbon atoms. If the carbon number of such an alkyl group exceeds 10, purification becomes difficult. Moreover, from the viewpoint of making purification easier, the carbon number of the alkyl group that can be selected as such multiple R ⁴ is more preferably 1 to 5, and even more preferably 1 to 3. Moreover, the alkyl group that can be selected as such multiple R ⁴ may be linear or branched.

Moreover, the cycloalkyl group that can be selected as R ⁴ in the general formula (3) is a cycloalkyl group having 3 to 10 carbon atoms. If the carbon number of such a cycloalkyl group exceeds 10, purification becomes difficult. Moreover, the carbon number of the cycloalkyl group that can be selected as such a plurality of R ^4s is more preferably 3 to 8, and even more preferably 5 to 6, from the viewpoint of easier purification.

Furthermore, the alkenyl group that can be selected as R ⁴ in the general formula (3) is an alkenyl group having 2 to 10 carbon atoms. If the carbon number of such an alkenyl group exceeds 10, purification becomes difficult. Moreover, the number of carbon atoms of the alkenyl group that can be selected as such multiple R ^4s is more preferably 2 to 5, and even more preferably 2 to 3, from the viewpoint of easier purification.

Moreover, the aryl group that can be selected as R ⁴ in the general formula (3) is an aryl group having a carbon number of 6 to 20. If the carbon number of such an aryl group exceeds 20, purification becomes difficult. Moreover, the number of carbon atoms of the aryl group that can be selected as such a plurality of R ^4s is more preferably 6 to 10, and even more preferably 6 to 8, from the viewpoint of easier purification.

Moreover, the aralkyl group that can be selected as R ⁴ in the general formula (3) is an aralkyl group having a carbon number of 7 to 20. If the carbon number of such an aralkyl group exceeds 20, purification becomes difficult. Moreover, the number of carbon atoms of the aralkyl group that can be selected as such a plurality of R ^4s is more preferably 7 to 10, and even more preferably 7 to 9, from the viewpoint of easier purification.

Furthermore, from the viewpoint of facilitating purification, the multiple R ^4s in the general formula (3) are each preferably independently a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a t-butyl group, a cyclohexyl group, an allyl group, a phenyl group, or a benzyl group, more preferably a methyl group, an ethyl group, or an n-propyl group, further preferably a methyl group or an ethyl group, and particularly preferably a methyl group. Note that the multiple R ^4s in the general formula (3) may be the same or different, but from the viewpoint of synthesis, it is more preferable that they are the same.

In addition, R ¹ , R ² , R ³ and R ⁴ in the general formula (4) have the same meanings as R ¹ , R ² , R ³ and R ⁴ in the general formula (3), respectively, and the preferred meanings thereof are also the same.

The carbonyl compound (B) may contain a compound having an endo/exo stereostructure and a compound having an exo/endo stereostructure, but the carbonyl compound (B) may contain either one of the compounds alone, or may contain both of them.

The tetracarboxylic dianhydride of the present invention is composed of the carbonyl compound (A) and/or the carbonyl compound (B), and the content of the carbonyl compound (A) relative to the total amount of the carbonyl compounds (A) and (B) is 30 to 100 mol % in terms of molar ratio. By making the content of the carbonyl compound (A) equal to or higher than the lower limit, when an acid anhydride is produced using the carbonyl compound and the resulting acid anhydride is used as a monomer to produce a polyimide, not only can a higher level of heat resistance be achieved, but the polymerization reactivity of the monomer can also be further improved.

Furthermore, the content of carbonyl compound (A) relative to the total amount of carbonyl compounds (A) and (B) is more preferably 40 to 100 mol%, even more preferably 60 to 100 mol%, particularly preferably 80 to 100 mol%, and most preferably 90 to 100 mol%. When the content of carbonyl compound (A) is within the above-mentioned preferred range, when an acid anhydride is produced using this and then used as a monomer to produce a polyimide, it is possible to further improve the heat resistance of the polyimide.

(Method for Producing Carbonyl Compounds)
A method that can be suitably adopted as a method for producing the carbonyl compound of the present invention will be described. The method for producing such a carbonyl compound is not particularly limited, but for example, a method for producing a carbonyl compound represented by the following general formula (10):

[In the formula, ^R1 and ^R2 are the same as ^R1 and ^R2 in the above formula (3) (the preferred values thereof are also the same).]
(a norbornene-based compound having an exo-type stereostructure in which a vinyl group is bonded to the exo position; hereinafter, sometimes simply referred to as "starting compound (I)") is reacted with an alcohol and carbon monoxide to obtain a compound represented by the following general formula (11):

[In the formula, R ¹ , R ² and R ⁴ have the same meanings as R ¹ , R ² and R ⁴ in the above formula (3) (the preferred meanings are also the same).
(Note that, since such a compound is used as a raw material in the following step (2), hereinafter, it may be simply referred to as "raw material compound (II)");
A mixture of the raw material compound (II) and optionally substituted dicyclopentadiene is heated to a temperature of 150° C. or higher to react with each other, thereby obtaining a compound represented by the following formula (12):

[In the formula, R ¹ , R ² , R ³ and R ⁴ are respectively defined as R ¹ , R ² , R ³ and R ⁴ in the above formula (3) (the preferred values thereof are also defined as above).]
and a compound having an exo/exo stereostructure represented by the following formula (13):

[In the formula, R ¹ , R ² , R ³ and R ⁴ are respectively defined as R ¹ , R ² , R ³ and R ⁴ in the above formula (3) (the preferred values thereof are also defined as above).]
and (2) obtaining a carbonyl compound precursor comprising a compound having an endo/exo stereostructure represented by the formula:
a step (3) of reacting the carbonyl compound precursor with an alcohol and carbon monoxide in the presence of a palladium catalyst and an oxidizing agent to obtain a carbonyl compound consisting of the carbonyl compound (A) and the carbonyl compound (B), and then adjusting the content of the carbonyl compound (A) as necessary to obtain the carbonyl compound of the present invention;
Hereinafter, steps (1) to (3) will be described separately.

Regarding step (1):
Step (1) is a step of reacting a raw material compound (I) with an alcohol and carbon monoxide to obtain the raw material compound (II).

The raw material compound (I) used in step (1) is a norbornene-based compound having an exo-type stereostructure in which a vinyl group is bonded to the exo position, as represented by the above formula (10). The method for producing such raw material compound (I) is not particularly limited, and a known method (for example, the method described in "Bull. Chem. Soc. Jpn., vol. 60, p. 1954-p. 1956 (1987)") can be appropriately adopted. R ¹ and R ² in the above formula (10) are respectively defined as R ¹ and R ² in the above formula (3), and the preferred ones are also defined as the same.

The alcohol used in step (1) is not particularly limited. From the viewpoint of ease of purification, the alcohol represented by the following general formula (14):
R ^a OH (14)
[In the formula, R ^a is an atom or group other than a hydrogen atom that can be selected as R ⁴ in the general formula (11).]
In other words, as such an alcohol, it is preferable to use an alkyl alcohol having 1 to 10 carbon atoms, a cycloalkyl alcohol having 3 to 10 carbon atoms, an alkenyl alcohol having 2 to 10 carbon atoms, an aryl alcohol having 6 to 20 carbon atoms, or an aralkyl alcohol having 7 to 20 carbon atoms.

Specific examples of such alcohols include methanol, ethanol, butanol, allyl alcohol, cyclohexanol, and benzyl alcohol. Among these, methanol and ethanol are more preferred, and methanol is particularly preferred, from the viewpoint of facilitating purification of the resulting compound. Moreover, such alcohols may be used alone or in combination of two or more.

In the present invention, the norbornene-based compound represented by the general formula (10) is reacted with the alcohol (preferably R ^a OH) and carbon monoxide (CO) in the presence of a palladium catalyst and an oxidizing agent to form an olefin group represented by the following general formula (15):
-COOR ^a (15)
[In the formula, R ^a is an atom or group other than a hydrogen atom that can be selected as R ⁴ in the general formula (11).]
It is possible to introduce an ester group represented by the formula (11) (R ⁴ may be the same or different for each position where the ester group is introduced), thereby obtaining a compound represented by the formula (11) (raw material compound (II)). In this way, in the present invention, in the presence of a palladium catalyst and an oxidizing agent, an alcohol (preferably R ^a OH) and carbon monoxide (CO) are used to introduce an ester group into the carbon of the olefin moiety in the norbornene ring (hereinafter, such a reaction may be simply referred to as an "esterification reaction" in some cases), thereby obtaining the raw material compound (II) represented by the formula (11). In addition, the conditions that can be adopted in such an esterification reaction are not particularly limited, and known conditions adopted in the reaction of introducing an ester group into the carbon of the olefin moiety in the norbornene ring can be appropriately adopted (for example, conditions similar to those adopted in the esterification method described in WO 2018/147373 can be adopted).

The palladium catalyst used in such an esterification reaction is not particularly limited, and a known catalyst containing palladium (for example, the catalyst described in WO 2018/147373) can be appropriately used, and examples thereof include inorganic acid salts of palladium, organic acid salts of palladium, and catalysts in which palladium is supported on a carrier. Suitable examples of such palladium catalysts include palladium chloride, palladium nitrate, palladium sulfate, palladium acetate, palladium propionate, palladium carbon, palladium alumina, palladium black, and palladium acetate having a nitrite ligand (formula: Pd ₃ (CH ₃ COO) ₅ (NO ₂ )).

In addition, as such a palladium catalyst, it is preferable to use a palladium catalyst (hereinafter, sometimes simply referred to as "Pd 3 (OAc) 5 (NO 2 )") containing palladium acetate having a nitrite ligand (catalyst represented by the formula: Pd ₃ (CH ₃ COO) ₅ (NO ₂ )) from the viewpoint that the production of by-products can be more sufficiently suppressed and the compound represented by the general formula ( ₁₁ ) _can be produced with higher selectivity. In addition, the method for producing such palladium acetate having a nitrite ligand (Pd ₃ (OAc) ₅ (NO ₂ )) is not particularly limited, _and a known method can be appropriately used, for example, the method described in Dalton Trans (vol. 11) published on June 7, 2005, pages 1989 to 1992 (authors: Vladimir I, Bakhmutov, et al.) or the like may be appropriately used.

The oxidizing agent used in the esterification reaction may be any oxidizing agent capable of oxidizing ^{Pd 0 to Pd 2+ when Pd 2+ in the palladium catalyst is reduced to Pd 0 in the esterification} reaction. Such an oxidizing agent is not particularly limited, and examples thereof include copper compounds, iron compounds, etc. Specific examples of such an oxidizing agent include cupric chloride, cupric nitrate, cupric sulfate, cupric acetate, ferric chloride, ferric nitrate, ferric sulfate, ferric acetate, etc.

Furthermore, the amount of alcohol used in such an esterification reaction is not particularly limited as long as it is an amount that allows the compound represented by the general formula (11) to be obtained. For example, the alcohol may be added in an amount greater than the amount theoretically required (theoretical amount) to obtain the compound represented by the general formula (11), and the excess alcohol may be used as it is as a solvent.

In the esterification reaction, it is sufficient that the carbon monoxide is supplied to the reaction system in the required amount. Therefore, it is not necessary to use high-purity carbon monoxide gas as the carbon monoxide, and a mixed gas of carbon monoxide and a gas inert to the esterification reaction (e.g., nitrogen) may be used. The pressure of such carbon monoxide is not particularly limited, but is preferably from normal pressure (approximately 0.1 MPa [1 atm]) to 10 MPa.

Furthermore, the method of supplying the carbon monoxide to the reaction system is not particularly limited, and any known method can be appropriately adopted. For example, a method of supplying carbon monoxide by bubbling into a mixed liquid containing the alcohol, the compound represented by the general formula (10), and the palladium catalyst, or a method of supplying carbon monoxide to the reaction system by introducing carbon monoxide into the atmospheric gas in a reaction vessel when a reaction vessel is used, etc. can be appropriately adopted.

In the esterification reaction, the amount of the palladium catalyst used is preferably an amount such that the molar amount of palladium in the palladium catalyst is 0.001 to 0.1 times (more preferably 0.001 to 0.01 times) the molar amount of the norbornene-based compound represented by the general formula (10). The amount of the oxidizing agent used is preferably 2 to 16 times (more preferably 2 to 8 times, and even more preferably 2 to 6 times) the molar amount of the norbornene-based compound represented by the general formula (10).

A solvent may be used in the reaction (esterification reaction) of the norbornene compound represented by the general formula (10) with alcohol and carbon monoxide. There are no particular limitations on the solvent, and any known solvent that can be used in an esterification reaction may be used as appropriate, such as hydrocarbon solvents such as n-hexane, cyclohexane, benzene, and toluene. In addition, since an acid is by-produced from the oxidizing agent in the esterification reaction, a base may be added to remove the acid. As such a base, a fatty acid salt such as sodium acetate, sodium propionate, or sodium butyrate is preferable. The amount of such a base used may be adjusted as appropriate depending on the amount of acid generated, etc.

The reaction temperature conditions for the esterification reaction are not particularly limited, but are preferably 0°C to 200°C (more preferably 0°C to 100°C, even more preferably about 10 to 60°C, and particularly preferably about 20 to 50°C). If the reaction temperature exceeds the upper limit, the yield tends to decrease, while if it is below the lower limit, the reaction rate tends to decrease. The reaction time for the esterification reaction is not particularly limited, but is preferably about 30 minutes to 24 hours.

The atmospheric gas in the esterification reaction is not particularly limited, and any gas usable in the esterification reaction can be appropriately used. For example, it may be a gas inert to the esterification reaction (nitrogen, argon, etc.), carbon monoxide, or a mixed gas of carbon monoxide and other gases (nitrogen, air, oxygen, hydrogen, carbon dioxide, argon, etc.). From the viewpoint of not affecting the catalyst or the oxidizing agent, carbon monoxide, a gas inert to the esterification reaction, or a mixed gas of carbon monoxide and a gas inert to the esterification reaction is preferred. When a method of introducing carbon monoxide by bubbling is adopted as a method of supplying carbon monoxide to the mixed liquid, for example, the atmospheric gas may be made of a gas inert to the esterification reaction before the reaction, and the reaction may be started by the above-mentioned bubbling, so that the atmospheric gas is a mixed gas of carbon monoxide and a gas inert to the esterification reaction, and the reaction may proceed as a result.

Furthermore, the pressure conditions in the esterification reaction (atmospheric gas pressure conditions: when the reaction is carried out in a reaction vessel, the gas pressure conditions in the vessel) are not particularly limited, but are preferably 0.05 MPa to 15 MPa, more preferably normal pressure (0.1 MPa [1 atm]) to 15 MPa, even more preferably 0.1 MPa to 10 MPa, and particularly preferably 0.11 MPa to 5 MPa.

By allowing the esterification reaction to proceed in this manner, it is possible to obtain a carbonyl compound (tetraester compound) represented by the general formula (11) in which all R ^4s in formula (11) are groups other than a hydrogen atom. When producing a carbonyl compound represented by the general formula (11) in which all R ^4s in formula (11) are hydrogen atoms, after the group represented by the formula -COOR ^a is introduced by the esterification reaction, the group may be converted into a group represented by the formula -COOH in which R ^a is a hydrogen atom by hydrolysis treatment or ester exchange reaction with a carboxylic acid. The method of such a reaction is not particularly limited, and a known method capable of converting a group represented by the formula -COOR ^a (ester group) into a formula -COOH (carboxy group) may be appropriately adopted.

In this manner, step (1) is carried out to esterify the olefin moiety in the norbornene ring in the raw material compound (I), thereby obtaining raw material compound (II). The raw material compound (II) is a norbornane-based compound having an exo-type stereostructure in which a vinyl group is bonded to the exo position, and is a compound represented by the above formula (11). When obtaining such raw material compound (II), in cases where by-products are present in the crude product obtained by carrying out step (1), it may be appropriately purified by adopting a known method. R ¹ , R ² and R ⁴ in formula (11) are respectively synonymous with R ¹ , R ² and R ⁴ in formula (3), and the preferred ones are also synonymous.

Regarding step (2):
In step (2), a mixture of the raw material compound (II) and optionally substituted dicyclopentadiene is heated to a temperature of 150° C. or higher to react with each other, thereby obtaining the carbonyl compound precursor. In this step, the raw material compound (II) obtained in step (1) is used.

The optionally substituted dicyclopentadiene used in step (2) is dicyclopentadiene or a compound in which at least a part of the hydrogen atoms in dicyclopentadiene has been substituted with a substituent. Examples of such a substituent include one selected from the group consisting of alkyl groups having 1 to 10 carbon atoms, which are groups that may be selected as ^R3 in the formula (3). By using such a dicyclopentadiene which may have a substituent, a cyclopentadiene which may have a substituent (a group which may be selected as R ³ in the formula (3)) can be produced in the system upon heating (one molecule of the dicyclopentadiene which may have a substituent is thermally decomposed to produce two molecules of cyclopentadiene which may have a substituent), and by reacting such cyclopentadiene with the raw material compound (II) (Diels-Alder reaction), it is possible to obtain a carbonyl compound precursor including a compound having an exo/exo stereostructure represented by the formula (12) above, and a compound having an endo/exo stereostructure represented by the formula (13) above and its enantiomer (a compound having an exo/endo stereostructure).

In this way, step (2) is a step for obtaining the desired carbonyl compound precursor by using optionally substituted dicyclopentadiene as a material for producing optionally substituted cyclopentadiene, and reacting the optionally substituted cyclopentadiene produced in the system by heating with the raw material compound (II) through the Diels-Alder reaction.

In this step (2), first, a mixture of the raw material compound (II) and optionally substituted dicyclopentadiene is prepared. In this mixture, the content ratio of the raw material compound (II) and optionally substituted dicyclopentadiene is not particularly limited, but it is preferable that the molar ratio ([raw material compound (II)]:[optionally substituted dicyclopentadiene]) is 1:0.5 to 1:1. By using each component in such a ratio, it is possible to more efficiently proceed with the reaction.

In step (2), a solvent may be further added to the mixture and the mixture may be heated in the solvent to allow the reaction to proceed. Although there are no particular limitations on the solvent, organic solvents that can be used in the so-called Diels-Alder reaction may be suitably used, such as alcohol-based solvents (including glycol-based solvents, glycerin-based solvents, and other polyhydric alcohol-based solvents), cellosolve-based solvents, ether-based solvents, amide-based solvents, and nitrile-based solvents. When the mixture contains a solvent, it is preferable to use the solvent so that the total amount of the raw material compound (II) and optionally substituted dicyclopentadiene in the mixture is about 10 to 50 mass%.

In step (2), the mixture is heated to a temperature of 150°C or higher (more preferably a temperature of 160 to 200°C). If the heating temperature is below the lower limit, it becomes difficult to thermally decompose the optionally substituted dicyclopentadiene to produce the optionally substituted cyclopentadiene, making it difficult to efficiently obtain the carbonyl compound precursor.

When heating and reacting in this way (Diels-Alder reaction), a pressurized vessel such as an autoclave may be used. In this case, heating may be started at normal pressure, or at a predetermined pressure.

In this way, the various conditions (including the heating temperature) in step (2) may be set so that the dicyclopentadiene which may have a substituent is thermally decomposed to produce a cyclopentadiene which may have a substituent in the system, and the Diels-Alder reaction can be induced between the produced cyclopentadiene which may have a substituent and the raw material compound (II). Any known conditions that can be used when carrying out a Diels-Alder reaction may be appropriately adopted.

In this manner, the mixture is heated to a temperature of 150° C. or higher to react, thereby obtaining a carbonyl compound precursor consisting of a compound having an exo/exo stereostructure represented by the above formula (12), a compound having an endo/exo stereostructure represented by the above formula (13), and a compound having an exo/endo stereostructure, which is its enantiomer. In formulas (12) and (13), R ¹ , R ² , R ³ and R ⁴ are respectively defined as R ¹ , R ² , R ³ and R ⁴ in the above formula (3), and the preferred values thereof are also defined as above.

Regarding step (3):
The step (3) is a step of reacting the carbonyl compound precursor with an alcohol and carbon monoxide in the presence of a palladium catalyst and an oxidizing agent to obtain a carbonyl compound consisting of the carbonyl compound (A) and the carbonyl compound (B), and then adjusting the content of the carbonyl compound (A) as necessary to obtain the carbonyl compound of the present invention.

In step (3), the carbonyl compound precursor is reacted with an alcohol and carbon monoxide in the presence of a palladium catalyst and an oxidizing agent in the same manner and under the same conditions as in the "esterification reaction" described in step (1) except that the carbonyl compound precursor is used instead of the raw material compound (I). Therefore, the same palladium catalyst, oxidizing agent, etc. as those described in step (1) can be used.

In this way, by esterifying the carbonyl compound precursor (introducing an ester group to the carbon atom of the olefin moiety in the norbornene ring contained in the carbonyl compound precursor), it is possible to obtain a compound containing at least one carbonyl compound (B) selected from the group consisting of the carbonyl compound (A) having the exo/exo stereostructure and/or the compound having the endo/exo stereostructure and its mirror image, that is, the compound having the exo/endo stereostructure.

In step (3), the carbonyl compound of the present invention is obtained by adjusting the content of the carbonyl compound (A) as necessary for the compound obtained by the esterification reaction. Here, "adjusting the content of the carbonyl compound (A) as necessary" means that even if the content of the compound (A) is not adjusted, if the carbonyl compound obtained after the esterification reaction has a content of the carbonyl compound (A), which is a type of stereoisomer, of 30 mol% or more, the carbonyl compound obtained will correspond to the carbonyl compound of the present invention without the need to carry out a step of adjusting the content of the isomer, and in that case, it is not necessary to carry out a step of adjusting the content of the isomer. At the same time, if the carbonyl compound obtained after the reaction (compound before adjusting the content of the stereoisomer) has a content of the carbonyl compound (A), which is a type of stereoisomer, of less than 30 mol%, or if it is necessary to increase the content of the carbonyl compound (A) to a higher level as desired depending on the application, etc., it means that a step of adjusting the content of the isomer may be carried out to obtain a carbonyl compound with a higher content of the carbonyl compound (A).

The process for adjusting the content of the carbonyl compound (A) in the compound obtained by the esterification reaction is not particularly limited. For example, a method of adjusting the content of the carbonyl compound (A) by sublimation purification can be adopted, taking advantage of the fact that the carbonyl compound (A) has a higher sublimation temperature than the carbonyl compound (B). For example, a method of adjustment using a so-called kugelrohr can be adopted. In this case, after the compound for which the content of the isomer is to be adjusted is sublimated, the types of isomers that tend to precipitate and remain in the high-temperature ball (kugel) that is first cooled and in the ball (kugel) on the lower temperature side differ depending on the difference in sublimation temperature for each isomer. Based on the ratio of the isomers in the compound precipitated in each kugel, a method of appropriately adjusting the content ratio to the desired ratio can be adopted. In this way, the carbonyl compound of the present invention can be obtained by adjusting the content of the carbonyl compound (A) to 30 mol % or more with respect to the total amount of the carbonyl compounds (A) and (B).

In addition, when producing a carbonyl compound in which all ^R4s in the formula are hydrogen atoms, after the group represented by the above formula: ^-COORa is introduced by the esterification reaction, such a group may be converted into a group represented by the formula: -COOH in which ^Ra is a hydrogen atom by hydrolysis treatment or ester exchange reaction with a carboxylic acid. The method of such a reaction is not particularly limited, and any known method capable of converting a group represented ^by the formula: -COORa (ester group) into a formula: -COOH (carboxy group) can be appropriately adopted.

(Method for Producing Tetracarboxylic Dianhydrides)
A method that can be suitably employed as a method for producing the tetracarboxylic dianhydride of the present invention will be described. The method for producing the tetracarboxylic dianhydride of the present invention includes, for example, a step (1) of reacting a compound represented by the general formula (10) (starting compound (I)) with an alcohol and carbon monoxide in the presence of a palladium catalyst and an oxidizing agent to obtain a compound represented by the general formula (11) (starting compound (II));
a step (2) of heating a mixture of the raw material compound (II) and dicyclopentadiene which may have a substituent at a temperature of 150° C. or higher to react with each other, thereby obtaining a carbonyl compound precursor including a compound having an exo/exo stereostructure represented by the formula (12) and a compound having an endo/exo stereostructure represented by the formula (13) and/or a compound having an exo/endo stereostructure which is an enantiomer thereof;
a step (3') of reacting the carbonyl compound precursor with an alcohol and carbon monoxide in the presence of a palladium catalyst and an oxidizing agent to obtain a carbonyl compound consisting of the carbonyl compound (A) and the carbonyl compound (B);
(4) a step of heating the carbonyl compound in a carboxylic acid having 1 to 5 carbon atoms using an acid catalyst to obtain a tetracarboxylic acid dianhydride composed of the acid dianhydride (A) and the acid dianhydride (B), and then adjusting the content of the acid dianhydride (A) as necessary to obtain the carbonyl compound of the present invention;
Each step will be described below separately.

Regarding steps (1) to (3')
In this method, steps (1) and (2) are the same as steps (1) and (2) described in the above-mentioned method for producing a carbonyl compound. Step (3') is the same as the steps described in the above-mentioned method for producing a carbonyl compound, except that the carbonyl compound precursor is esterified to obtain the carbonyl compound directly without carrying out the step of "adjusting the content of carbonyl compound (A)" which is adopted as necessary.

Regarding step (4):
Step (4) is a step of heating a carbonyl compound (a carbonyl compound consisting of the above carbonyl compound (A) and the above carbonyl compound (B): hereinafter sometimes referred to as "raw material compound (III)") in a carboxylic acid having 1 to 5 carbon atoms using an acid catalyst (heating step) to obtain a tetracarboxylic acid dianhydride consisting of the above acid dianhydride (A) and the above acid dianhydride (B), and then adjusting the content of the acid dianhydride (A) as necessary to obtain the tetracarboxylic acid dianhydride of the present invention.

The acid catalyst used in step (4) is not particularly limited, and may be either a homogeneous acid catalyst or a heterogeneous acid catalyst (solid catalyst). Among such acid catalysts, a homogeneous acid catalyst is preferred from the viewpoint of ease of purification.

There are no particular limitations on such homogeneous acid catalysts, and known homogeneous acid catalysts that can be used in reactions to convert carboxylic acids to anhydrides or ester compounds to acid anhydrides can be used as appropriate. From the viewpoint of improving the reaction yield, such homogeneous acid catalysts are more preferably trifluoromethanesulfonic acid, tetrafluoroethanesulfonic acid, nonafluorobutanesulfonic acid, and chlorodifluoroacetic acid, and even more preferably trifluoromethanesulfonic acid and tetrafluoroethanesulfonic acid. Note that such homogeneous acid catalysts may be used alone or in combination of two or more.

The amount of the acid catalyst (more preferably a homogeneous acid catalyst) used is not particularly limited, but is preferably such that the molar amount of the acid in the acid catalyst is 0.001 to 2.00 molar equivalents (more preferably 0.01 to 1.00 molar equivalents) relative to the amount (molar amount) of the carbonyl compound (raw material compound (III)). If the amount of the acid catalyst used is less than the lower limit, the reaction rate tends to decrease, while if it exceeds the upper limit, purification becomes somewhat difficult and the purity of the product tends to decrease. The molar amount of the acid in the acid catalyst referred to here is the molar amount calculated in terms of functional groups (e.g., sulfonic acid groups (sulfo groups) and carboxylic acid groups (carboxy groups)) in the acid catalyst.

The amount of the acid catalyst (more preferably a homogeneous acid catalyst) used is preferably 0.1 to 100 parts by mass, more preferably 1 to 20 parts by mass, per 100 parts by mass of the carbonyl compound (raw material compound (III)). If the amount of such an acid catalyst used is less than the lower limit, the reaction rate tends to decrease, while if it exceeds the upper limit, side reaction products tend to be more easily generated.

Furthermore, in this method, the carbonyl compound is heated in a carboxylic acid having 1 to 5 carbon atoms using the acid catalyst (heating step). Thus, in the heating step, a carboxylic acid having 1 to 5 carbon atoms (hereinafter sometimes simply referred to as a "lower carboxylic acid") is used. Examples of such lower carboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, etc., and among them, from the viewpoint of ease of production and purification, formic acid, acetic acid, and propionic acid are preferred, and formic acid and acetic acid are more preferred. Such lower carboxylic acids may be used alone or in combination of two or more. In addition, the amount of such lower carboxylic acids (e.g., formic acid, acetic acid, propionic acid) used is not particularly limited, but it is preferably 4 to 100 times the molar amount of the carbonyl compound (raw material compound (III)).

In addition, in such a method, since the carbonyl compound (raw material compound (III)) is heated in the lower carboxylic acid, it is preferable to incorporate the carbonyl compound in the lower carboxylic acid. The content of the carbonyl compound in such a lower carboxylic acid is preferably 1 to 40% by mass, and more preferably 2 to 30% by mass.

In this method, when the carbonyl compound (raw material compound (III)) is a compound (tetracarboxylic acid) in which R ⁴ in the formula is a hydrogen atom, a reaction (forward reaction) in which a tetracarboxylic dianhydride and water are produced from the carbonyl compound (tetracarboxylic acid) proceeds by the heating step. The forward reaction and the reverse reaction in which the carbonyl compound (tetracarboxylic acid) is produced from the tetracarboxylic dianhydride and water are equilibrium reactions. In this method, when the carbonyl compound is a compound in which R ⁴ in the formula is a group other than a hydrogen atom, a reaction (forward reaction) in which a tetracarboxylic dianhydride, an ester compound of a lower carboxylic acid, and water are produced from the carbonyl compound and the lower carboxylic acid proceeds by the heating step. The forward reaction and the reverse reaction in which the carbonyl compound and the lower carboxylic acid are produced from the carboxylic anhydride, an ester compound of a lower carboxylic acid, and water are equilibrium reactions. Therefore, in such a heating step, it is possible to efficiently proceed with the reaction (forward reaction) by appropriately changing the concentrations of the components in the system.

In addition, the conditions (including heating temperature, atmospheric conditions, etc.) that can be adopted in such a heating step are not particularly limited, and as long as the method (conditions) are such that the carbonyl compound (raw material compound (III)) can be heated in the lower carboxylic acid using the acid catalyst, thereby converting the ester group and/or carboxy group (carboxylic acid group) in the carbonyl compound into an acid anhydride group, the conditions can be appropriately adopted. For example, conditions that are adopted in known reactions that can form an acid anhydride group (for example, conditions for forming an acid anhydride described in WO 2018/147373, etc.) can be appropriately used.

In addition, in such a heating step, it is preferable to first prepare a mixture of the lower carboxylic acid, the carbonyl compound, and the acid catalyst so that heating in the lower carboxylic acid is possible. The method of preparing such a mixture is not particularly limited, and it may be prepared appropriately depending on the device used in the heating step, for example, by adding (introducing) them into the same container. In addition, in such a heating step, other solvents may be added to the lower carboxylic acid. Examples of such solvents (other solvents) include aromatic solvents such as benzene, toluene, xylene, and chlorobenzene; ether solvents such as ether, THF, and dioxane; ester solvents such as ethyl acetate; hydrocarbon solvents such as hexane, cyclohexane, heptane, and pentane; nitrile solvents such as acetonitrile and benzonitrile; halogen solvents such as methylene chloride and chloroform; ketone solvents such as acetone and MEK; and amide solvents such as DMF, NMP, DMI, and DMAc.

The temperature conditions for heating the carbonyl compound (raw material compound (III)) in the lower carboxylic acid are not particularly limited, but it is preferable to set the upper limit of the heating temperature to 180°C (more preferably 150°C, even more preferably 140°C, and particularly preferably 130°C), and the lower limit of the heating temperature to 80°C (more preferably 100°C, and even more preferably 110°C). It is also preferable to set such a heating temperature to a temperature lower than the boiling point of the homogeneous acid catalyst within the above temperature condition range.

The heating step may further include a step of refluxing the mixture (a mixture of the lower carboxylic acid, the carbonyl compound, and the acid catalyst) by heating, from the viewpoint of producing the tetracarboxylic acid anhydride more efficiently. In this way, by including a reflux step in the heating step, it becomes possible to produce the carboxylic acid anhydride more efficiently.

Here, the degree of progress of the forward reaction can be determined by checking the amount of by-products (e.g., water and ester compounds of low carboxylic acids) contained in the steam. Therefore, when performing the reflux process, the reflux time may be appropriately set so that the reaction proceeds efficiently while checking the amount of by-products (e.g., ester compounds of low carboxylic acids) in the steam, and then the distillate component removal process may be performed while heating. By performing the distillate component removal process in this way, by-products (e.g., ester compounds of low carboxylic acids and water) can be removed from the reaction system, making it possible to proceed with the forward reaction more efficiently. In addition, during the distillate component removal process, if the amount of low carboxylic acid decreases when the distillate components (steam) are appropriately distilled off (for example, if ester compounds of low carboxylic acids and water are generated as by-products, carboxylic acid is consumed, and the amount of carboxylic acid decreases as a result of distilling off the steam), it is preferable to appropriately add (continuously add in some cases) the amount of low carboxylic acid that has decreased and then heat it. In addition, when such a heating step includes a step of refluxing the mixture, the reflux conditions are not particularly limited, and known conditions can be appropriately adopted, and can be appropriately changed to suitable conditions depending on the type of carbonyl compound (raw material compound) used, etc.

The pressure conditions (pressure conditions during the reaction) when the carbonyl compound (raw material compound (III)) is heated in the lower carboxylic acid are not particularly limited, and the reaction can proceed under any conditions, such as normal pressure, pressurized conditions, or reduced pressure conditions. For example, when the above-mentioned reflux step is employed, the reaction can be carried out under pressurized conditions using vapor of the lower carboxylic acid as the solvent. The pressure conditions are preferably 0.001 to 10 MPa, and more preferably 0.1 to 1.0 MPa.

The atmospheric gas used when the carbonyl compound (raw material compound (III)) is heated in the lower carboxylic acid is not particularly limited, and may be, for example, air or an inert gas (nitrogen, argon, etc.). In order to efficiently volatilize the by-products (lower carboxylic acid ester compounds and water) produced in the reaction and to make the reaction proceed more efficiently (to make the equilibrium reaction of the ester exchange more favorable to the product system), the above gas (preferably an inert gas such as nitrogen or argon) may be bubbled or stirred while being ventilated into the gas phase of the reactor (reaction vessel).

The heating time for heating the carbonyl compound (raw material compound (III)) in the lower carboxylic acid is not particularly limited, but is preferably 0.5 to 100 hours, and more preferably 1 to 50 hours. In addition, when heating the carbonyl compound (raw material compound (III)) in the lower carboxylic acid, the reaction may be carried out while stirring the lower carboxylic acid into which the carbonyl compound has been introduced (more preferably a mixture of the lower carboxylic acid, the carbonyl compound, and the acid catalyst) from the viewpoint of uniformly proceeding with the reaction.

Furthermore, in the step of heating the carbonyl compound (raw material compound (III)) in the lower carboxylic acid (heating step), it is preferable to use acetic anhydride together with the lower carboxylic acid. When using such acetic anhydride, the amount of acetic anhydride used is not particularly limited, but is preferably 4 to 100 times the molar amount of the carbonyl compound (raw material compound (III)).

Even when acetic anhydride is used in this way, it is preferable to adopt the conditions for the temperature, pressure, atmospheric gas, heating time, etc., during heating as explained in the heating step. Also, when acetic anhydride is used in this way, it is preferable that the heating step is a step of refluxing the mixture. When acetic anhydride is used in this way and reflux is performed, it is possible to sufficiently proceed with the reaction by only performing the reflux step without performing steps such as distilling off steam or adding a lower carboxylic acid depending on the amount used, etc., and it is also possible to more efficiently produce tetracarboxylic dianhydride.

By carrying out such a heating step, a tetracarboxylic acid dianhydride consisting of the acid dianhydride (A) and the acid dianhydride (B) can be obtained from the carbonyl compound (raw material compound (III)).

In step (4), the content of the acid dianhydride (A) in the tetracarboxylic dianhydride obtained by the heating step is adjusted as necessary to obtain the tetracarboxylic dianhydride of the present invention. Here, the term "as necessary" in the step of adjusting the content of the acid dianhydride (A) means that, even if the content of the acid dianhydride (A) is not adjusted, when a tetracarboxylic dianhydride is obtained by the heating step in which the content of the acid dianhydride (A), which is a type of stereoisomer, is 30 mol % or more relative to the total amount of the acid dianhydride (A) and the acid dianhydride (B), the obtained tetracarboxylic dianhydride corresponds to the tetracarboxylic dianhydride of the present invention without the step of adjusting the content of the isomer. This means that it is not necessary to carry out a content adjustment step, and also means that in cases where the tetracarboxylic dianhydride obtained by the heating step (compound before the stereoisomer content adjustment) has a content of the acid dianhydride (A), which is one type of stereoisomer, less than 30 mol% relative to the total amount of the acid dianhydride (A) and the acid dianhydride (B), or when it is necessary to increase the content of the acid dianhydride (A) to a higher level as desired depending on the application, etc., a content adjustment step of the isomer may be carried out to obtain a tetracarboxylic dianhydride having a higher content of the acid dianhydride (A).

The process for adjusting the content of the acid dianhydride (A) is not particularly limited, but for example, a method of adjusting the content of the acid dianhydride (A) by sublimation purification can be adopted, taking advantage of the fact that the sublimation temperature of the acid dianhydride (A) is higher than that of the acid dianhydride (B). For example, a method of adjustment using a so-called Kugelrohr can be adopted. In this case, after the tetracarboxylic dianhydride for adjusting the content of the isomer is sublimated, the type of isomer that is likely to precipitate and remain in the high-temperature ball (kugel) that is first cooled and the ball (kugel) on the lower temperature side differs depending on the sublimation temperature of each isomer, and a method of appropriately adjusting the content ratio to the desired ratio based on the ratio of isomers in the compound precipitated in each kugel can be adopted. In this way, the carbonyl compound of the present invention can be obtained by obtaining a tetracarboxylic dianhydride in which the content of the acid dianhydride (A) is 30 mol % or more relative to the total amount of the acid dianhydrides (A) and (B).

The above describes a method that can be suitably employed as a method for producing the tetracarboxylic dianhydride of the present invention based on a method including steps (1) to (4). However, the method for producing the tetracarboxylic dianhydride of the present invention is not limited to the above method. For example, a method may be employed in which the carbonyl compound of the present invention is prepared in advance, and the carbonyl compound of the present invention is heated in a carboxylic acid having 1 to 5 carbon atoms using an acid catalyst to obtain the tetracarboxylic dianhydride of the present invention. Note that the heating step in such a method (a step of heating in a carboxylic acid having 1 to 5 carbon atoms using an acid catalyst) is preferably the same as the heating step described in step (4) above.

[Polyimide]
The polyimide of the present invention is characterized in that it contains at least one repeating unit (B) consisting of a repeating unit (A) having an exo/exo type stereostructure represented by the above general formula (5) and/or a structural unit (repeating unit) having an endo/exo type stereostructure represented by the above general formula (6) and a structural unit (repeating unit) having an exo/endo type stereostructure which is its enantiomer, and that the content of the repeating unit (A) relative to the total amount of the repeating units (A) and (B) is 30 to 100 mol % in terms of molar ratio. The repeating unit (B) may contain a structural unit (repeating unit) having an endo/exo type stereostructure alone, may contain a structural unit (repeating unit) having an exo/endo type stereostructure alone, or may contain both of them.

R ¹ , R ² and R ³ in such general formulas (5) and (6) are the same as R ¹ , R ² and R ³ in the above general formula (1), and the preferred ones are also the same as R ¹ , R ² and R ³ in the above general formula (1). In such general formulas (5) and (6), the multiple R ^1s may be the same or different, but from the viewpoint of ease of purification, it is preferable that they are the same. Furthermore, in general formulas (5) and (6), R ² and R ³ may be the same or different, but from the viewpoint of ease of purification, it is preferable that they are the same.

The arylene group that can be selected as R ⁵ in the general formulas (5) and (6) is an arylene group having 6 to 50 carbon atoms. The number of carbon atoms in such an arylene group is preferably 6 to 40, more preferably 6 to 30, and even more preferably 12 to 20. If the number of carbon atoms is less than the lower limit, the heat resistance of the polyimide tends to decrease, while if the number of carbon atoms exceeds the upper limit, the solubility of the obtained polyimide in a solvent tends to decrease, and the moldability into a film or the like tends to decrease.

R ⁵ (an arylene group having 6 to 50 carbon atoms) in the repeating units represented by the general formulas (5) and (6) is represented by the following formula (16):
H ₂ NR ₅ -NH ₂ (16)
[In formula (16), R ⁵ represents an arylene group having 6 to 50 carbon atoms.]
(Thus, it is preferable to use the diamine compound represented by the above formula (16) as a raw material compound and introduce R ⁵ into the repeating unit as the residue.) Such a diamine compound (raw material compound used to introduce R ⁵ into the repeating unit) is not particularly limited, and known diamine compounds (for example, aromatic diamines described in WO 2018/147373) can be appropriately used. Examples of such diamine compounds include 1,4-diaminobenzene, 1,3-diaminobenzene, 2,4-diaminotoluene, 2,5-diaminotoluene, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 2,4'-diaminodiphenyl ether, 2,2'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,7-diamino-dimethyldibenzothiophene-5,5-di oxide, 4,4'-diaminobenzanilide, 3,3'-diaminobenzophenone, bis(4-aminophenyl)sulfide, 1,3-bis(4-aminophenoxy)propane, 1,4-bis(4-aminophenoxy)butane, 1,5-bis(4-aminophenoxy)pentane, 1,3-bis(4-aminophenoxy)-2,2-dimethylpropane, 1,2-bis[2-(4-aminophenoxy)ethoxy]ethane, 9,9-bis(4-aminophenyl)fluorene, 5(6)-amino-1-(4-aminomethyl)-1,3,3-trimethylindane, 1,4-bis(4-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzyl benzene, 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 3,3'-dicarboxy-4,4'-diaminodiphenylmethane, 4,6-dihydroxy-1,3-phenylenediamine, 3,3'-dihydroxy-4,4'-diaminobiphenyl, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 3,3',4,4'-tetraaminobiphenyl, 1,3-bis(3-aminopropyl)tetramethylphenyl Examples of the diamine compounds include tetramethyldisiloxane 1,6-diaminohexane, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, 4,4'-methylenebis(4-cyclohexylamine), trans-1,4-cyclohexanediamine, bicyclo[2.2.1]heptanebis(methylamine), tricyclo[3.3.1.13,7]decane-1,3-diamine, 4-aminobenzoic acid 4-aminophenyl, 2-(4-aminophenyl)aminobenzoxazole, 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene, 2,2'-bis(3-sulfopropoxy)-4,4'-diaminobiphenyl, 4,4'-bis(4-aminophenoxy)biphenyl-3,3'-disulfonic acid, and bis(4-aminophenyl)terephthalate. These diamine compounds may be used alone or in combination of two or more.

In addition, the diamine compound used as a raw material compound for simply repeatedly introducing R ⁵ into the compound is preferably 2,2-bis[4-(4-aminophenoxy)phenyl]propane (abbreviation: BAPP), 2,2'-bis(trifluoromethyl)benzidine (abbreviation: TFMB), 4,4'-diaminobenzanilide (abbreviation: DABAN), p-phenylenediamine (abbreviation: PPD), bis(4-aminophenyl)terephthalate (abbreviation: BPTP), 4,4'-diaminodiphenyl ether (abbreviation: ODA), 1,3-diaminobenzene, 9,9-bis(4-aminophenyl)fluorene, or 4-aminobenzoic acid 4-aminophenyl, more preferably BAPP, ODA, BPTP, DABAN, PPD, or TFMB. The method for producing such a diamine compound is not particularly limited, and a known method can be appropriately adopted. In addition, a commercially available diamine compound may be appropriately used.

The polyimide of the present invention contains a repeating unit (A) having an exo/exo type stereostructure represented by the above general formula (5), and/or at least one repeating unit (B) selected from the group consisting of a structural unit (repeating unit) having an endo/exo type stereostructure represented by the following general formula (6) and a structural unit (repeating unit) having an exo/endo type stereostructure that is its mirror image, and the content of the repeating unit (A) relative to the total amount of the repeating units (A) and (B) is 30 to 100 mol % in molar ratio.

In this way, the content of the repeating unit (A) having an exo/exo type stereostructure is 30 to 100 mol% based on the total molar amount of the repeating units (A) and (B). By setting the content of such repeating unit (A) to be equal to or higher than the lower limit, a higher level of heat resistance can be obtained. From the viewpoint of obtaining a higher level of mechanical strength, the content of the repeating unit (A) based on the total molar amount of the repeating units (A) and (B) is more preferably 40 to 100 mol%, even more preferably 60 to 100 mol%, particularly preferably 80 to 100 mol%, and most preferably 90 to 100 mol%.

Such a polyimide of the present invention is preferably made of a polycondensate of an acid dianhydride monomer containing the tetracarboxylic dianhydride of the present invention and the diamine compound. By using the tetracarboxylic dianhydride of the present invention as a raw material and polycondensing it with the diamine compound, a polyimide containing the repeating unit (A) and/or the repeating unit (B) and having a content of the repeating unit (A) of 30 to 100 mol % based on the total molar amount of the repeating units (A) and (B) can be efficiently obtained.

In addition, such polyimides preferably contain the repeating unit (A) and/or the repeating unit (B) (more preferably, the total amount of repeating units (A) and (B) is 50 to 100 mol % (even more preferably 70 to 100 mol %, particularly preferably 80 to 100 mol %, most preferably 90 to 100 mol %) of all repeating units in the polyimide). In addition, such polyimides may contain other repeating units as long as the effects of the present invention are not impaired. Such other repeating units are not particularly limited, and include known repeating units that can be used as repeating units of polyimides, such as repeating units derived from tetracarboxylic dianhydrides other than the tetracarboxylic dianhydride of the present invention and the diamine compound. In this way, for example, when the polyimide of the present invention is a polycondensation product of an acid dianhydride monomer containing the tetracarboxylic acid dianhydride of the present invention and the diamine compound, the other repeating units can be easily introduced into the polyimide by making the acid dianhydride monomer contain the tetracarboxylic acid dianhydride of the present invention and another tetracarboxylic acid dianhydride other than the tetracarboxylic acid dianhydride of the present invention.

Such other tetracarboxylic dianhydrides are not particularly limited, and known tetracarboxylic dianhydrides that can be used in the production of polyimides can be appropriately used. For example, pyromellitic anhydride, 3,4'-oxydiphthalic dianhydride, 4,4'-oxydiphthalic dianhydride, biphenyl-3,4,3',4'-tetracarboxylic dianhydride, benzophenone-3,4,3',4'-tetracarboxylic dianhydride, diphenylsulfone-3,4,3',4'-tetracarboxylic dianhydride, 4,4'-(2,2-hexafluoroisopropylidene)diphthalic dianhydride, m-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, p-terphenyl-3,4,3',4'-tetracarbo dianhydride, cyclobutane-1,2,3,4-tetracarboxylic dianhydride, 3-carboxymethyl-1,2,4-cyclopentanetricarboxylic acid 1,4:2,3-dianhydride, cyclohexane-1,2,4,5-tetracarboxylic dianhydride, butane-1,2,3,4-tetracarboxylic dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid) 1,4-phenylene, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic dianhydride (CpODA), the following formulas (17) to (18):

The compound represented by the above formula (17) (abbreviated as "BNBDA"), the compound represented by the above formula (18) (abbreviated as "BzDA"), etc. can be used. One of these other tetracarboxylic dianhydrides may be used alone, or two or more of them may be used in combination.

When the polyimide contains other repeating units in addition to the repeating units (A) and (B), the molar ratio thereof ([total amount of the repeating units (A) and (B)]: [other repeating units]) may be 99.9:0.1 to 0.1:99.9. Furthermore, when other repeating units are contained, it is preferable that the ratio of the total amount (total amount) of the repeating units (A) and (B) to the content of the other repeating units be 9:1 to 5:5 (more preferably 9:1 to 7:3) in terms of the heat resistance and transparency of the resulting polyimide.

The polyimide of the present invention preferably has a 5% weight loss temperature of 450°C or more, more preferably 460 to 520°C. If the 5% weight loss temperature is less than the lower limit, high heat resistance cannot be obtained, while if it exceeds the upper limit, it tends to be difficult to manufacture polyimide with such properties. The 5% weight loss temperature can be determined by increasing the temperature from room temperature (25°C) to 40°C while flowing nitrogen gas in a nitrogen gas atmosphere, heating at a rate of 10°C/min. from 40°C as the starting temperature, and measuring the temperature at which the weight of the sample used decreases by 5%. In addition, it is preferable to use a sample with a mass of 1.0 mg to 10 mg (more preferably 1.5 mg to 4.0 mg) during measurement. By setting the mass of the sample in the above range, the same value can be measured for the same polyimide even if the mass of the sample is changed.

In addition, such polyimides preferably have a glass transition temperature (Tg) of 300°C or higher, and particularly preferably 330 to 450°C. If the glass transition temperature (Tg) is below the lower limit, it tends to be difficult to achieve sufficient heat resistance, while if it exceeds the upper limit, it tends to be difficult to produce polyimides with such properties. The glass transition temperature (Tg) can be measured in tension mode using a thermomechanical analyzer (manufactured by Rigaku under the trade name "TMA8310").

In addition, such polyimides preferably have a linear expansion coefficient (CTE) of 0 to 100 ppm/K, more preferably 10 to 60 ppm/K. If such a linear expansion coefficient exceeds the upper limit, when combined with a metal or inorganic substance having a linear expansion coefficient in the range of 5 to 20 ppm/K to form a composite, peeling tends to occur due to thermal history. In addition, if the linear expansion coefficient is less than the lower limit, the solubility and film properties tend to decrease. To measure the linear expansion coefficient of such polyimides, a polyimide film having a size of 20 mm in length and 5 mm in width (the thickness of such a film does not affect the measured value and is not particularly limited, but it is preferable to set it to 10 to 30 μm) is formed as a measurement sample, and a thermomechanical analyzer (Rigaku's product name "TMA8310") is used as the measurement device, and the conditions are adopted: in a nitrogen atmosphere, in a tensile mode (49 mN), and at a heating rate of 5°C/min, and the average value obtained by calculating the average change in length per 1°C in the temperature range of 100°C to 200°C is adopted.

Furthermore, such polyimides preferably have a softening temperature of 300°C or higher, more preferably 330 to 450°C. If the softening temperature is below the lower limit, it tends to be difficult to achieve sufficient heat resistance, while if it exceeds the upper limit, it tends to be difficult to manufacture polyimides with such properties. Such softening temperatures can be measured in penetration mode using a thermomechanical analyzer (manufactured by Rigaku under the trade name "TMA8310"). In addition, since the size of the sample (length, width, thickness, etc.) does not affect the measured value, the size of the sample can be appropriately adjusted to a size that can be attached to the jig of the thermomechanical analyzer (manufactured by Rigaku under the trade name "TMA8310") used.

In addition, such polyimides preferably have a thermal decomposition temperature (Td) of 450°C or more, more preferably 460 to 520°C. If the thermal decomposition temperature (Td) is less than the lower limit, it tends to be difficult to achieve sufficient heat resistance, while if it exceeds the upper limit, it tends to be difficult to produce polyimides with such properties. The thermal decomposition temperature (Td) can be determined by measuring the temperature at the intersection of the tangents drawn on the decomposition curves before and after thermal decomposition under conditions of a nitrogen atmosphere and a heating rate of 10°C/min. using a TG/DTA220 thermogravimetric analyzer (manufactured by SII Nano Technology Co., Ltd.). In addition, it is preferable to use a sample with a mass of 1.0 to 10 mg (more preferably 5 mg to 10 mg) during measurement. By setting the mass of the sample to the above range, the same value can be measured for the same polyimide even if the mass of the sample is changed. Furthermore, such thermal decomposition temperature (Td) can also be measured simultaneously using the same device and under the same conditions (under a nitrogen atmosphere, heating rate of 10°C/min.) as for measuring the 5% weight loss temperature.

Furthermore, the number average molecular weight (Mn) of such polyimide is preferably 1000 to 1,000,000 in polystyrene equivalent. If the number average molecular weight is less than the lower limit, sufficient heat resistance tends to be difficult to achieve, while if it exceeds the upper limit, processing tends to be difficult. Furthermore, the weight average molecular weight (Mw) of such polyimide is preferably 1000 to 5,000,000 in polystyrene equivalent. If the weight average molecular weight is less than the lower limit, sufficient heat resistance tends to be difficult to achieve, while if it exceeds the upper limit, processing tends to be difficult. Furthermore, the molecular weight distribution (Mw/Mn) of such polyimide is preferably 1.1 to 5.0. If the molecular weight distribution is less than the lower limit, production tends to be difficult, while if it exceeds the upper limit, production of a uniform film tends to be difficult. The molecular weight (Mw or Mn) and molecular weight distribution (Mw/Mn) of such polyimide can be obtained by converting the measured data into polystyrene using gel permeation chromatography as a measuring device. In addition, in the case of such polyimides, if it is difficult to measure the molecular weight, the molecular weight, etc. may be inferred based on the viscosity of the polyamic acid used to produce the polyimide, and a polyimide may be selected and used according to the application, etc.

In addition, from the viewpoint of obtaining a higher degree of transparency, such polyimides are more preferably those having a total light transmittance of 80% or more (more preferably 85% or more, particularly preferably 87% or more). In addition, from the viewpoint of obtaining a higher degree of transparency, such polyimides are more preferably those having a haze (turbidity) of 5 to 0 (more preferably 4 to 0, particularly preferably 3 to 0). In addition, from the viewpoint of obtaining a higher degree of transparency, such polyimides are more preferably those having a yellowness index (YI) of 5 to 0 (more preferably 4 to 0, particularly preferably 3 to 0). Such total light transmittance, haze (turbidity) and yellowness index (YI) can be easily achieved by appropriately selecting the type of polyimide, etc. In addition, such total light transmittance and haze (turbidity) can be measured using a measuring device manufactured by Nippon Denshoku Industries Co., Ltd. under the trade name "Haze Meter NDH-5000" and a film made of polyimide having a thickness of 5 to 80 μm as a measurement sample. The yellowness index can be measured by using a measurement device manufactured by Nippon Denshoku Industries Co., Ltd. under the trade name of "Spectrophotometer SD6000" and a film made of polyimide having a thickness of 5 to 80 μm as a measurement sample. The total light transmittance, haze (turbidity), and yellowness index (YI) can be measured from the same polyimide because the film made of polyimide having a thickness of 5 to 80 μm is sufficiently thin and does not affect the measured values. Therefore, a film having a thickness within the above range may be used to measure the total light transmittance, haze (turbidity), and yellowness index (YI). The length and width of the measurement sample may be any size that can be placed at the measurement site of the measurement device, and the length and width may be changed as appropriate. The total light transmittance is determined by measuring in accordance with JIS K7361-1 (published in 1997), the haze (turbidity) is determined by measuring in accordance with JIS K7136 (published in 2000), and the yellowness index (YI) is determined by measuring in accordance with ASTM E313-05 (published in 2005).

Such polyimides preferably have an elongation at break of 5% or more. If the elongation at break is less than the lower limit, the toughness is low and the polyimide tends to be mechanically brittle. The elongation at break can be measured according to the method described in "JIS K7161" of the Japanese Industrial Standards.

The shape of such polyimide is not particularly limited, and may be, for example, a film or powder, or may be extruded into pellets. In this way, the polyimide of the present invention may be formed into a film or pellets by extrusion, or may be appropriately molded into various shapes by known methods.

When the polyimide of the present invention is made into a film, the form of the film (polyimide film) is not particularly limited, and it may be in the form of a film, and can be appropriately designed into various shapes (disk-like, cylindrical (film processed into a cylindrical shape), etc.). The thickness of such a polyimide film (film made of the polyimide of the present invention) is not particularly limited, but is preferably 1 to 500 μm, and more preferably 5 to 200 μm. If the thickness is less than the lower limit, the strength tends to decrease and handling tends to become difficult, while if the thickness exceeds the upper limit, multiple coatings may be required or processing may become complicated.

Such polyimide may be dissolved in an organic solvent and used as a polyimide resin solution (varnish). The organic solvent used in such a polyimide resin solution (a resin solution containing the polyimide of the present invention and an organic solvent) may be the same as the organic solvent used in the method for producing a polyimide precursor resin described below.

In addition, the applications in which the polyimide of the present invention can be used are not particularly limited, and the polyimide can be appropriately applied to known applications in which polyimide can be used. In addition, since the polyimide of the present invention has a sufficiently high degree of transparency and a higher degree of heat resistance, it can be used in a wide range of applications, including films for flexible wiring boards, heat-resistant insulating tapes, electric wire enamels, semiconductor coating agents (e.g., protective coating agents for semiconductors), liquid crystal alignment films, transparent conductive films for organic electroluminescence (EL) films, films for organic electroluminescence (EL) lighting, flexible substrate films, substrate films for flexible organic electroluminescence (EL) films, front films for flexible displays, back films for flexible displays, polyimide belts, coating agents, barrier films, sealing materials, interlayer insulating materials, passivation films, TAB (Tape Automated Brazing), etc. Bonding) tape, optical waveguide, flexible transparent conductive film, transparent conductive film for organic thin-film solar cell, transparent conductive film for dye-sensitized solar cell, flexible gas barrier film, film for touch panel, seamless polyimide belt for copier (so-called transfer belt), transparent electrode substrate (transparent electrode substrate for organic EL, transparent electrode substrate for solar cell, transparent electrode substrate for electronic paper, etc.), interlayer insulating film, sensor substrate, substrate for image sensor, reflector for light-emitting diode (LED) (reflector for LED lighting: LED reflector), cover for LED lighting, cover for LED reflector lighting, coverlay film, highly ductile composite substrate, resist for semiconductor, lithium ion battery, substrate for organic memory, substrate for organic transistor, substrate for organic semiconductor, material for color filter, etc. In addition to the above-mentioned uses, such polyimide can be appropriately used for, for example, automobile parts, aerospace parts, bearing parts, sealant, bearing parts, gear wheel and valve parts, etc., by making the shape into a powder or various molded bodies, by utilizing its sufficiently high heat resistance. Furthermore, such polyimides can have a lower dielectric tangent (tan δ) depending on their structure. Therefore, when the polyimide of the present invention is used, for example, as an insulating film material for semiconductors or as a substrate film for flexible printed circuit boards (FPCs), it is possible to sufficiently reduce transmission loss. Therefore, the polyimide of the present invention can be suitably used as a high-frequency band material (for example, a large-scale integrated circuit (LSI) or an electronic circuit). A method for producing such a polyimide will be described later. The polyimide of the present invention has been described above, and the polyimide precursor resin of the present invention will be described below.

[Polyimide precursor resin]
The polyimide precursor resin of the present invention contains a repeating unit (A') having an exo/exo stereostructure represented by the above general formula (7), and/or at least one repeating unit (B') selected from the group consisting of a structural unit (repeating unit) having an endo/exo stereostructure represented by the above general formula (8) and a structural unit (repeating unit) having an exo/endo stereostructure which is its enantiomer, and the content of the repeating unit (A') relative to the total amount of the repeating units (A') and (B') is 30 to 100 mol %.

The polyimide precursor resin can be imidized (for example, when the polyimide precursor resin is a polyamic acid, it can be imidized and subjected to dehydration ring closure to form the polyimide of the present invention. The polyimide precursor resin containing the repeating units (A') and/or (B') can be formed based on the tetracarboxylic dianhydride of the present invention and the diamine compound.

R ¹ , R ² , R ³ and R ⁵ in the above general formulas (7) and (8) are the same as ¹ , R ² , R ³ and R ⁵ in the above general formulas (5) and (6). The multiple R ^1s in the general formulas (7) and (8) may be the same or different, but are preferably the same from the viewpoint of ease of purification. Furthermore, R ² and R ³ in the general formulas (7) and (8) may be the same or different, but are preferably the same from the viewpoint of ease of purification.

In the general formulas (7) and (8), the carbon atom a (carbon atom with symbol a) forming the norbornane ring is bonded to one of the bonds represented by *1 and *2, and the carbon atom b (carbon atom with symbol b) forming the norbornane ring is bonded to the other of the bonds represented by *1 and *2. In the general formulas (7) and (8), the carbon atom c (carbon atom with symbol c) forming the norbornane ring is bonded to one of the bonds represented by *3 and *4, and the carbon atom d (carbon atom with symbol d) forming the norbornane ring is bonded to the other of the bonds represented by *3 and *4. Each of the bonds represented by *1 to *4 may take an exo or endo configuration relative to the norbornane ring to which it is bonded. There are no particular limitations on the configuration of the bonds represented by *1 to *4, but from the viewpoint of further improving reactivity and further reducing the linear expansion coefficient, it is preferable that all of them take an exo configuration.

In addition, when the polyimide precursor resin is obtained under mild reaction conditions, the bonds *1 to *4 in the repeating unit usually have an exo configuration relative to the norbornane methylene head. This is because, when the polyimide precursor resin is formed under mild reaction conditions, the configuration of the raw material compound (the acid dianhydride ring bonded to the norbornane ring basically has an exo configuration relative to the norbornane methylene head) is maintained, and the bonds *1 to *4 have an exo configuration relative to the norbornane methylene head. In this way, by maintaining the exo configuration, it is possible to more efficiently proceed with the imidization reaction (condensation reaction) process when forming a polyimide using a polyimide precursor resin having such a configuration. Furthermore, the configuration of the bonds *1 and *3 relative to the polymer main chain may be cis or trans, and the configuration of the bonds *2 and *4 depends on the configuration of the bonds *1 and *3, but may also be cis or trans. It is generally known that physical properties such as the linear expansion coefficient are improved when the bond *1 and bond *3 are in a trans configuration relative to the polymer main chain.

In the above general formulas (7) and (8), Y ¹ is each independently any one of a hydrogen atom, an alkyl group having 1 to 6 carbon atoms (preferably 1 to 3 carbon atoms), or an alkylsilyl group having 3 to 9 carbon atoms. The type of the substituent of ^{Y 1} and the introduction rate of the substituent can be changed by appropriately changing the production conditions. When all such Y ¹ are hydrogen atoms (when they become the so-called repeating units of polyamic acid), the production of polyimide tends to be easy.

Furthermore, when Y ¹ in the above general formulas (7) and (8) is an alkyl group having 1 to 6 carbon atoms (preferably 1 to 3 carbon atoms), the storage stability of the polyimide precursor resin tends to be more excellent. Furthermore, when Y ¹ is an alkyl group having 1 to 6 carbon atoms (preferably 1 to 3 carbon atoms), Y ¹ is more preferably a methyl group or an ethyl group.

Furthermore, when Y ¹ in the above general formulas (7) and (8) is an alkylsilyl group having 3 to 9 carbon atoms, the solubility of the polyimide precursor resin tends to be more excellent. When Y ¹ is an alkylsilyl group having 3 to 9 carbon atoms, Y ¹ is more preferably a trimethylsilyl group or a t-butyldimethylsilyl group.

Such polyimide precursor resins can be classified into 1) polyamic acids (wherein all of the Y ¹ in the general formula of the repeating units contained in the polyimide precursor resin are hydrogen atoms), 2) polyamic acid esters (wherein at least a portion of Y ¹ is an alkyl group), and 3) polyamic acid silyl esters (wherein at least a portion of Y ¹ is an alkylsilyl group) according to the type of substituent of Y 1 ⁱⁿ the repeating unit. Note that, as such polyimide precursor resins, polyamic acids in which all of the Y ¹ in the general formula of the repeating units (A') and/or (B') are hydrogen atoms are more preferred because they are easier to prepare.

In addition, when the polyimide precursor resin is a polyamic acid, the intrinsic viscosity [η] of the polyamic acid is preferably 0.05 to 3.0 dL/g, and more preferably 0.1 to 2.0 dL/g. If the intrinsic viscosity [η] is less than 0.05 dL/g, the resulting film tends to be brittle when a film-like polyimide is produced using the polyimide. On the other hand, if the intrinsic viscosity [η] exceeds 3.0 dL/g, the viscosity is too high and the processability is reduced, and it is difficult to obtain a uniform film when a film is produced. In addition, in this specification, the "intrinsic viscosity [η]" is a value measured as follows. That is, first, N,N-dimethylacetamide is used as a solvent, and the polyamic acid is dissolved in the N,N-dimethylacetamide to a concentration of 0.5 g/dL to obtain a measurement sample (solution). Next, the viscosity of the measurement sample is measured using a dynamic viscometer at a temperature condition of 30°C, and the obtained value is used as the intrinsic viscosity [η]. As such a kinematic viscometer, an Ostwald type viscometer (automatic viscosity measuring device manufactured by CANNON (product name "mini-PV-HX")) is used.

In addition, with respect to Y ¹ in the above general formulas (7) and (8), when a group other than a hydrogen atom (an alkyl group and/or an alkylsilyl group) is introduced, the introduction rate (the ratio of Y ¹ that is a group other than a hydrogen atom based on the total amount of Y ¹ ) is not particularly limited, but when at least a part of Y ¹ is an alkyl group and/or an alkylsilyl group, it is preferable that 25% or more (more preferably 50% or more, even more preferably 75% or more) of the total amount of ^Y 1 is an alkyl group and/or an alkylsilyl group (in this case, Y ¹ other than the alkyl group and/or the alkylsilyl group is a hydrogen atom). By making 25% or more of the total amount of Y ¹ an alkyl group and/or an alkylsilyl group, the storage stability of the polyimide precursor tends to be more excellent.

In addition, the polyimide precursor resin (more preferably polyamic acid) of the present invention has a molar ratio of 30 to 100 mol% of the repeating unit (A') relative to the total amount of the repeating units (A') and (B'). Thus, the content of the repeating unit (A') having an exo/exo type stereostructure is 30 to 100 mol% relative to the total molar amount of the repeating units (A') and (B'). By setting the content of such repeating unit (A') to the lower limit or more, when a polyimide is produced using this, a polyimide having a higher level of heat resistance can be obtained. In addition, the content of the repeating unit (A') relative to the total molar amount of the repeating units (A') and (B') is more preferably 40 to 100 mol%, even more preferably 60 to 100 mol%, particularly preferably 80 to 100 mol%, and most preferably 90 to 100 mol%, from the viewpoint of obtaining a higher level of mechanical strength.

Such a polyimide precursor resin (more preferably a polyamic acid) is preferably made of a polyaddition product or derivative thereof of an acid dianhydride monomer containing the tetracarboxylic dianhydride of the present invention and the diamine compound. By using the tetracarboxylic dianhydride of the present invention as a raw material and subjecting it to a polyaddition reaction with the diamine compound, a polyimide precursor resin containing the repeating unit (A') and/or the repeating unit (B') and having a content of the repeating unit (A') of 30 to 100 mol % relative to the total molar amount of the repeating units (A') and (B') can be efficiently obtained.

The polyimide precursor resin (more preferably polyamic acid) of the present invention preferably contains mainly repeating units consisting of the repeating unit (A') and/or the repeating unit (B') (even more preferably, the total amount of the repeating unit (A') and the repeating unit (B') is 50 to 100 mol% based on the total repeating units). In the polyimide precursor resin (more preferably polyamic acid) of the present invention, the total amount (total amount) of the repeating unit (A') and the repeating unit (B') is preferably 90 mol% or more, more preferably 95 to 100 mol%, and even more preferably 98 to 100 mol% based on the total repeating units contained in the polyimide precursor resin (more preferably polyamic acid).

In addition, such a polyimide precursor resin (more preferably polyamic acid) may contain other repeating units other than the repeating unit (A') and the repeating unit (B') within a range that does not impair the effects of the present invention. Such other repeating units are not particularly limited, and include known repeating units that can be used as repeating units of polyimide precursor resins (more preferably polyamic acid), such as repeating units derived from tetracarboxylic dianhydrides other than the tetracarboxylic dianhydride of the present invention and the diamine compound. In this way, when the polyimide precursor resin of the present invention is a polyaddition product of an acid dianhydride monomer containing the tetracarboxylic dianhydride of the present invention and the diamine compound, the acid dianhydride monomer can be easily introduced into the polyimide by containing the tetracarboxylic dianhydride of the present invention and other tetracarboxylic dianhydrides other than the tetracarboxylic dianhydride of the present invention. In addition, when such other repeating units are contained, the molar ratio ([total amount of the repeating units (A') and (B')]: [other repeating units]) may be 99.9:0.1 to 0.1:99.9. Furthermore, when other repeating units are included, the ratio of the total amount (total quantity) of the repeating units (A') and (B') to the content of the other repeating units is preferably set to a molar ratio ([total amount of the repeating units (A') and (B')]: [content of the other repeating units]) of 9:1 to 5:5 (more preferably 9:1 to 7:3) from the viewpoint of the heat resistance and transparency of the resulting polyimide.

Such a polyimide precursor resin (more preferably a polyamic acid) may be dissolved in an organic solvent to form a polyimide precursor resin solution (varnish). As the organic solvent used in such a polyimide precursor resin solution (a resin solution containing the polyimide precursor resin (more preferably a polyamic acid) of the present invention and an organic solvent), the same organic solvent as that used in the method for producing a polyimide precursor resin described later can be suitably used. Therefore, such a polyimide precursor resin solution may be prepared by carrying out the method for producing a polyimide precursor resin described later and using the reaction liquid obtained after the reaction as it is as a polyimide precursor resin solution.

The content of the polyimide precursor resin in such a polyimide precursor resin solution is not particularly limited, but is preferably 1 to 80% by mass, and more preferably 5 to 50% by mass. If the content is less than the lower limit, it tends to be difficult to produce a polyimide film, while if the content exceeds the upper limit, it also tends to be difficult to produce a polyimide film. Such a polyimide precursor resin solution can be suitably used to produce the polyimide of the present invention described above, and can be suitably used to produce polyimides of various shapes. For example, a polyimide in the form of a film can be easily produced by applying such a polyimide precursor resin solution onto various substrates, imidizing and curing the solution.

(Method for Producing the Polyimide Precursor Resin of the Present Invention)
A method that can be suitably employed for producing the polyimide precursor resin of the present invention will now be described.

The method for producing the polyimide precursor of the present invention is not particularly limited, and a method (reaction conditions, etc.) similar to a known method for producing a polyimide precursor (for example, the method described in paragraphs [0170] to [0200] of WO 2018/147373) can be appropriately adopted, except that the type of tetracarboxylic dianhydride is the tetracarboxylic dianhydride of the present invention. In addition, as a method for producing the polyimide precursor of the present invention, for example, a method in which the tetracarboxylic dianhydride of the present invention and the diamine compound (the diamine compound represented by the general formula (16)) are subjected to an addition polymerization reaction in the presence of an organic solvent to obtain a polyimide precursor can be mentioned as a suitable method.

The organic solvent used in such a method is preferably an organic solvent capable of dissolving both the tetracarboxylic dianhydride of the present invention and the diamine compound (more preferably, an organic solvent capable of dissolving the polyimide precursor to be formed). There are no particular limitations on such organic solvents, and any organic solvent that can be used in the production of polyimides can be used as appropriate, such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide, γ-butyrolactone (GBL), γ-caprolactone, tetramethylurea (N,N,N',N'-tetramethylurea: TMU), dimethylsulfoxide, and δ-valerolactone. Such organic solvents may be used alone or in combination of two or more.

The amount of the organic solvent used is preferably such that the total amount of monomers used in the reaction (the total amount of the tetracarboxylic dianhydride of the present invention and the diamine compound) is 5 to 40% by mass (more preferably 10 to 25% by mass) relative to the total amount of the reaction solution. The amount of the diamine compound used is preferably such that the number of moles of the diamine compound is 0.9 to 1.1 moles when the total amount of the tetracarboxylic dianhydride used in the reaction is converted to 1 mole, and from the viewpoint of being able to further increase the degree of polymerization, it is more preferable to use an amount such that the number of moles of the diamine compound is 0.95 to 1.05 moles.

The reaction temperature when the tetracarboxylic dianhydride of the present invention and the diamine compound are subjected to the addition polymerization reaction may be appropriately adjusted to a temperature at which the addition polymerization reaction can proceed, and is not particularly limited, but is preferably 15 to 100° C. In addition, when such an addition polymerization reaction is performed, a method may be adopted in which, for example, a solution containing the tetracarboxylic dianhydride and the diamine compound is reacted at the reaction temperature while being stirred at atmospheric pressure or under an inert atmosphere such as nitrogen, helium, or argon for 3 to 100 hours. In this way, by proceeding with the addition polymerization reaction between the tetratetracarboxylic dianhydride of the present invention and the diamine compound, it is possible to obtain a polyamic acid (polyimide precursor in which Y ¹ in formulas (7) and (8) is a hydrogen atom) suitable as the polyimide precursor of the present invention.

Here, as a manufacturing method for producing a polyimide precursor resin containing a repeating unit (II) in which Y ¹ in formulas (7) and (8) is other than a hydrogen atom, a known method may be appropriately adopted depending on the design. For example, except that the tetracarboxylic acid dianhydride of the present invention is used as the tetracarboxylic acid dianhydride, a method similar to a known method (reaction conditions, etc.) such as the method described in paragraphs [0170] to [0200] of WO 2018/147373 and the method described in paragraphs [0165] to [0174] of WO 2018/066522 can be appropriately adopted.

(Method for Producing the Polyimide of the Invention)
The method for producing the polyimide of the present invention is not particularly limited, and for example, except for using the tetracarboxylic dianhydride of the present invention as a tetracarboxylic dianhydride, a known method for producing a polyimide by reacting a tetracarboxylic dianhydride with a diamine compound (for example, the method described in WO 2011/099518, the method described in WO 2015/163314, the method described in JP-A 2018-044180, the method described in WO 2018/066522, the method described in WO 2018/147373, the method described in WO 2018/051888, etc.) The same method (reaction conditions, etc.) can be appropriately adopted.

In addition, as a method that can be suitably used as a method for producing the polyimide of the present invention, for example, a method in which a polyimide precursor resin (preferably polyamic acid (polyamic acid)) is formed as described above, and then the polyimide precursor resin is subjected to ring-closing condensation (dehydration ring-closing: intramolecular condensation) to imidize it to obtain a polyimide can be exemplified. In this way, the method (conditions, etc.) for imidizing a polyimide precursor resin (preferably polyamic acid) by ring-closing condensation is not particularly limited, and the method (conditions) used in the known imidization method (for example, the method described in WO 2011/099518, the method described in WO 2015/163314, the method described in JP 2018-044180, the method described in WO 2018/066522, the method described in WO 2018/147373, the method described in WO 2018/051888, etc.) can be appropriately adopted. Examples of the method for imidization include a method of imidizing the polyamic acid by heating it at a temperature of 60 to 400°C (more preferably 150 to 350°C) or a method of imidizing the polyamic acid using a so-called "imidizing agent". There are no particular limitations on the imidizing agent, and known agents can be used as appropriate. Examples of such agents include acid anhydrides such as acetic anhydride, propionic anhydride, and trifluoroacetic anhydride; and tertiary amines such as pyridine, collidine, lutidine, triethylamine, and N-methylpiperidine. In addition, when imidizing the polyamic acid using an imidizing agent, the reaction temperature during imidization is preferably -40°C to 200°C (more preferably 30 to 150°C).

In addition, in a method that can be suitably used as a method for producing the polyimide of the present invention, the tetracarboxylic dianhydride of the present invention and the diamine compound are heated in an organic solvent in the presence of a reaction accelerator to react with each other, thereby forming the polyimide precursor resin and the subsequent ring-closing condensation (imidization) simultaneously as a series of reactions to form a polyimide. This makes it possible to efficiently produce polyimide by simultaneously forming an intermediate polyimide precursor resin (preferably polyamic acid) and the subsequent polyimide formation (imidization). In addition, when such a method is adopted, depending on the type of polyimide, it is also possible to obtain polyimide in the form of a polyimide resin solution (polyimide varnish) after its production. In this way, the method of forming the polyimide precursor resin and the subsequent ring-closing condensation (imidization) simultaneously as a series of reactions to form a polyimide is not particularly limited, and a known method (for example, the method described in International Publication No. 2018/051888, etc.) can be appropriately adopted. In addition, when such a method is adopted, the organic solvent can be the same as that described in the method for producing the polyimide precursor resin described above. Furthermore, the reaction accelerator is not particularly limited, and known ones (for example, those described in WO 2018/051888, etc.) can be appropriately used. For example, triethylamine, diisopropylethylamine, N-methylpiperidine, and pyridine can be mentioned as suitable ones. Such reaction accelerators may be used alone or in combination of two or more kinds. In addition, the heating temperature when heating in an organic solvent in the presence of a reaction accelerator is not particularly limited, but is preferably 150 to 200°C.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

The molecular structures of the compounds obtained in the examples and comparative examples described below were identified by appropriate infrared absorption spectroscopy (IR measurement), nuclear magnetic resonance spectroscopy (NMR measurement), etc., depending on the type of compound. Here, the IR and NMR measurements were performed using an IR measurement device (manufactured by Thermo Scientific, product name: Nicolet380 FT-IR spectrometer) and an NMR measurement device (manufactured by VARIAN, product name: UNITY INOVA-600), respectively.

<1> Synthesis of raw material compounds for carbonyl compounds (Synthesis Example 1: Synthesis of 2,3-di(methoxycarbonyl)-5-exo-vinylbicyclo[2.2.1]heptane)
First, methanol (500 g), CuCl ₂ (II) (59.2 g, 0.44 mol), exo-5-vinyl-2-norbornene (25.2 g, 0.21 mol), and Pd ₃ (OAc) ₅ (NO ₂ ) (122.1 mg, 0.54 mmol in terms of Pd) were added to a 1 L glass autoclave reactor to obtain a mixed solution. Note that the "exo-5-vinyl-2-norbornene" used in the preparation of the mixed solution is the same as that described in Bull. Chem. Soc. Jpn., published in 1987. (vol. 60), pp. 1954-1956, and "Pd ₃ (OAc) ₅ (NO 2 )" was prepared by adopting the method described in Dalton Trans (vol. 11) _, p. 1991, published in 2005 (note that all "Pd ₃ (OAc) ₅ (NO ₂ )" used in the following examples and the like described in this application were prepared by a similar method, and therefore the explanation of the preparation method will be omitted in the following description).

Next, the pressure inside the autoclave reactor was reduced to -0.08 MPaG, and carbon monoxide was introduced into the autoclave reactor to adjust the internal pressure to 0.03 MPaG. Next, the temperature inside the autoclave reactor was set to 25°C and the mixture was stirred for 4 hours, after which the temperature was gradually raised to 40°C while continuing stirring, and stirring was continued for another 4 hours at 40°C. After that, stirring of the mixture was stopped and the mixture was allowed to stand overnight (13.5 hours), yielding a reaction liquid as a brown suspension.

Next, the autoclave reactor was depressurized by removing the atmospheric gas containing carbon monoxide from the inside, and the atmospheric gas inside the autoclave reactor was replaced with nitrogen. Next, the temperature was raised to 50°C while flowing nitrogen into the inside of the autoclave reactor, and it was confirmed that the concentration of carbon monoxide in the gas (outlet gas) discharged from the autoclave reactor was 0 ppm. Thereafter, the temperature inside the autoclave reactor was further raised to 65°C to distill off methanol from the reaction liquid, thereby obtaining a solid content. Next, toluene (760 g) was added to the inside of the autoclave reactor in which the solid content had precipitated, and a mixture of the solid content and toluene was obtained. In order to completely remove methanol from the mixture, the pressure inside the autoclave reactor was reduced to -0.07 MPaG, and the temperature was raised to 73°C, and the solvent in the mixture was partially distilled off. Next, toluene (190 g) was further added to the mixture, and the mixture was heated to 80° C. with stirring and filtered to separate and recover the precipitate (solid content) and the filtrate. Next, the obtained precipitate was washed with toluene (190 g), and the washing liquid was added to the filtrate. Next, the filtrate was heated and held at a temperature of 80° C., and washed twice with 5% by mass hydrochloric acid (380 g), once with saturated sodium bicarbonate water (380 g), and once with ion-exchanged water (380 g). After washing in this way, the obtained organic layer was subjected to filter filtration to remove (separate) the solid content precipitated in the washing liquid, and an organic layer was obtained. Next, the solid content removed from the washing liquid was washed with toluene (190 g), and the washing liquid was added to the organic layer. Next, the organic layer thus obtained (the organic layer obtained by liquid separation purification) was concentrated under reduced pressure using an evaporator to obtain a crude product. The crude product thus obtained was then subjected to reduced pressure distillation to obtain a main fraction at a temperature of 113° C. and a pressure of 14 Pa. In order to confirm the structure of the main fraction thus obtained, IR measurement and NMR ( ¹ H-NMR, ¹³ C-NMR) measurement were performed, and it was found that the obtained product was a mixture of a compound represented by the following general formula (20) (compound name: 2,3-di(methoxycarbonyl)-5-exo-vinylbicyclo[2.2.1]heptane) and a compound represented by the following general formula (21) (compound name: 2,3-di(methoxycarbonyl)-5-ethylidenebicyclo[2.2.1]heptane).

The components in this mixture were then separated by preparative liquid chromatography to obtain 18 g (yield 36%) of 2,3-di(methoxycarbonyl)-5-exo-vinylbicyclo[2.2.1]heptane (the compound represented by the above general formula (20): the target product). The purity of the 2,3-di(methoxycarbonyl)-5-exo-vinylbicyclo[2.2.1]heptane obtained by this separation was determined by HPLC and GC measurements, and was found to be 99 area %.

(Synthesis Example 2: Synthesis of 2,2'-bi(bicyclo[2.2.1]heptane)-5'-ene-5,6'-dicarboxylic acid diester)
First, 2,3-di(methoxycarbonyl)-5-exo-vinylbicyclo[2.2.1]heptane (100 g, 0.42 mol) and dicyclopentadiene (31 g, 234 mmol), which were prepared by carrying out the same method as in Synthesis Example 1 several times, were added to a 500 mL capacity autoclave reactor to obtain a mixture. Next, nitrogen was introduced so that the gauge pressure in the autoclave reactor was 0.034 MPa (5 psig), and the internal temperature was raised to 180° C. and the mixture was stirred for 4 hours. After stirring in this manner, the internal temperature of the autoclave reactor was cooled to room temperature (25° C.) to precipitate solids in the reactor, and the precipitate (solids) was taken out by filtration. Next, the precipitate was washed three times with toluene (30 mL) and then vacuum dried at 60° C. to obtain 52 g of a product (crystals).

In order to confirm the structure of the product thus obtained, IR measurement and NMR ( ¹ H-NMR, ¹³ C-NMR) measurement were carried out, and it was found that the product thus obtained had the following general formula (22):

It was confirmed that the product was 2,2'-bi(bicyclo[2.2.1]heptane)-5'-ene-5,6'-dicarboxylic acid diester (hereinafter sometimes referred to as "BNBDE") represented by the following general formula (23), and the yield was 41%. The obtained BNBDE was confirmed to be a mixture of stereoisomer A (hereinafter sometimes referred to as "BNBDE-A"), which is a compound having an exo/exo type stereostructure represented by the following general formula (23), and stereoisomer B (hereinafter sometimes referred to as "BNBDE-B") consisting of a compound having an endo/exo type stereostructure represented by the following general formula (24) and its mirror image, a compound having an exo/endo type stereostructure. Note that the endo/exo type and the exo/endo type mirror image are indistinguishable from each other spectroscopically, so hereinafter, both are evaluated as "stereoisomer B". The content ratio (molar ratio) of BNBDE-A to BNBDE-B in the resulting mixture was 1/3 (BNBDE-A/BNBDE-B).

<2> Synthesis of carbonyl compound (Example 1)
First, methanol (470 g), CuCl ₂ (II) (59.2 g, 0.44 mol), BNBDE (63.9 g, 0.21 mol: mixture of BNBDE-A and BNBDE-B) prepared by carrying out the same method as in Synthesis Example 2 multiple times, and Pd ₃ (OAc) ₅ (NO ₂ ) (122.1 mg, 0.54 mmol in terms of Pd) were added to a glass autoclave reactor having a capacity of 1 L to obtain a mixed solution. Next, the inside of the autoclave reactor was depressurized to -0.08 MPaG, and carbon monoxide was introduced into the autoclave reactor to adjust the internal pressure to 0.03 MPaG. Next, the temperature inside the autoclave reactor was set to 25° C. and the mixture was stirred for 4 hours. Then, the temperature was gradually raised to 40° C. while continuing stirring, and stirring was continued for another 4 hours at a temperature condition of 40° C. After that, stirring of the mixture was stopped and the mixture was allowed to stand overnight (13.5 hours), thereby obtaining a reaction liquid as a brown suspension.

Next, the autoclave reactor was depressurized by removing the atmospheric gas containing carbon monoxide from inside, and the atmospheric gas inside the autoclave reactor was replaced with nitrogen. Next, the temperature was raised to 50°C while flowing nitrogen inside the autoclave reactor, and it was confirmed that the concentration of carbon monoxide in the gas (outlet gas) discharged from the autoclave reactor was 0 ppm. Thereafter, the temperature inside the autoclave reactor was further raised to 65°C to distill off methanol from the reaction liquid and obtain a solid content. Next, toluene (760 g) was added inside the autoclave reactor in which the solid content had precipitated, and a mixture of the solid content and toluene was obtained. In order to completely remove methanol from the mixture, the pressure inside the autoclave reactor was reduced to -0.07 MPaG, and the temperature was raised to 73°C, and the solvent in the mixture was partially distilled off. Next, toluene (190 g) was further added to the mixture, and the mixture was heated to 80° C. with stirring to perform filtration, and the precipitate (solid content) and the filtrate were separated and collected. Next, the obtained precipitate was washed with toluene (190 g), and the washing liquid was added to the filtrate. Next, the filtrate was heated and held at a temperature of 80° C., and washed twice with 5% by mass concentration hydrochloric acid (380 g), once with saturated sodium bicarbonate water (380 g), and once with ion-exchanged water (380 g). After washing in this way, the obtained organic layer was subjected to filter filtration to remove (separate) the solid content precipitated in the washing liquid, and an organic layer was obtained. Next, the solid content removed from the washing liquid was washed with toluene (190 g), and the washing liquid was added to the organic layer. Next, the organic layer thus obtained (the organic layer obtained by liquid separation purification) was concentrated under reduced pressure at 60° C. in an evaporator until the amount of toluene reached 440 g, to obtain a concentrated liquid. The concentrated solution was then slowly cooled to room temperature (25°C) to perform recrystallization, and solid matter (crystals) was precipitated. The solid matter (crystals) thus obtained was then filtered, washed four times with toluene (25 g), and vacuum dried at 60°C to obtain 66 g of product (white crystals).

In order to confirm the structure of the product thus obtained, IR measurement and NMR ( ¹ H-NMR, ¹³ C-NMR) measurement were carried out, and it was found that the product thus obtained had the following general formula (25):

It was confirmed that the product was 5,5'-bi-2-norbornene-5,5',6,6'-tetracarboxylic acid tetramethyl ester (hereinafter sometimes referred to as "BNBTE") represented by the formula (26) below, and the yield was 74%. The obtained BNBTE was confirmed to be a mixture of stereoisomer A (hereinafter sometimes referred to as "BNBTE-A"), which is a compound having an exo/exo type stereostructure represented by the following general formula (26), and stereoisomer B (hereinafter sometimes referred to as "BNBTE-B") consisting of a compound having an endo/exo type stereostructure represented by the following general formula (27) below and its enantiomer, a compound having an exo/endo type stereostructure. Note that the endo/exo type and the exo/endo type enantiomers are indistinguishable from each other spectroscopically, and therefore, hereinafter, both are evaluated as "stereoisomer B". The content ratio (molar ratio) of BNBTE-A to BNBTE-B in the resulting mixture was 1/3 (BNBTE-A/BNBTE-B).

<3-1> Synthesis of tetracarboxylic acid anhydride (Example 2)
Tetracarboxylic dianhydride was prepared using BNBTE (a mixture of BNBTE-A and BNBTE-B) obtained in Example 1 as follows. That is, first, a 1 L reaction vessel was purged with nitrogen, and BNBTE (34 g, 80.5 mmol) obtained in Example 1, acetic acid (0.49 kg), and trifluoromethanesulfonic acid (0.30 g, 2.00 mmol) were added to obtain a mixed solution. Next, the mixed solution was heated to 113° C. and maintained at that temperature (113° C.), and a step of distilling off steam (acetic acid, etc.) was carried out while dropping acetic acid with a pump so that the amount of liquid in the reaction vessel was constant. Next, the distillate distilled out of the system was analyzed by mass measurement and gas chromatography every hour to confirm the degree of progress of the reaction. It was confirmed by such analysis that acetic acid, methyl acetate, and water were present in the distillate. In this step, the distillation of methyl acetate stopped after 6 hours had elapsed since the start of the distillation of steam, so heating was stopped and the reaction solution was gradually cooled to room temperature (25° C.). Next, the reaction solution was concentrated using an evaporator to obtain a crude product.

The crude product thus obtained was then subjected to sublimation purification by the following method. That is, first, for purification, the crude product was placed in a Kugel distillation apparatus (Shibata Scientific, GTO-2000, number of cooling bulbs: 3) for purification. Next, at room temperature (25°C), the pressure inside the apparatus was reduced to 0.12 Torr, and the temperature was gradually raised in stages to 200°C and 250°C (with a heating rate of 10°C/min and held at 200°C and 250°C for 30 minutes each), and finally to 315°C. After the temperature reached 315°C by this heating, heating was continued for 1.5 hours and then returned to room temperature. After the temperature reached 315°C by this heating, heating was continued for 1.5 hours and then returned to room temperature. In this way, sublimation purification was performed, and the product (precipitate) was precipitated in the hottest ball (Kugel: hereinafter referred to as the "high temperature part") and the second coldest ball (Kugel: hereinafter referred to as the "low temperature part") of the three cooling balls in the Kugel apparatus. In this way, 4 g (yield 15%) of product was obtained from the high temperature part (hereinafter referred to as the "high temperature side product" for convenience), and 20 g (yield 75%) of product was obtained from the low temperature part (hereinafter referred to as the "low temperature side product" for convenience).

Next, in order to confirm the structure of the products (high-temperature side product and low-temperature side product) in each kugel (cooling ball), IR measurement and NMR ( ¹ H-NMR, ¹³ C-NMR) measurement were carried out. All of the products in each kugel (cooling ball) were found to be represented by the following general formula (28):

It was confirmed that the compound was 5,5'-bi-2-norbornene-5,5',6,6'-tetracarboxylic acid-5,5',6,6'-dianhydride (hereinafter sometimes referred to as "BNBDA") represented by the formula: In addition, taking into consideration the results of the above-mentioned structure confirmation (IR measurement, NMR measurement), etc., the low-temperature product contains stereoisomer A having an exo/exo type stereostructure represented by the following general formula (29) (hereinafter, sometimes referred to as "BNBDA-A") and stereoisomer B consisting of a compound having an endo/exo type stereostructure represented by the following general formula (30) and a compound having an exo/endo type stereostructure that is its mirror image (hereinafter, sometimes referred to as "BNBDA-B". Note that since the endo/exo type and the exo/endo type mirror images are indistinguishable from each other spectroscopically, both are evaluated as "stereoisomer B"). It was found to be a mixture containing BNBDA-A and BNBDA-B in a ratio of 1/10 based on the molar ratio (BNBDA-A/BNBDA-B). On the other hand, taking into consideration the results of the above structural confirmation (IR measurement, NMR measurement), the high-temperature product was found to be a compound containing 100 mol% BNBDA-A (BNBDA consisting only of stereoisomer A).

As a result of the NMR measurement performed to confirm the structure, the NMR data ( ¹ H-NMR and ¹³ C-NMR measurement results) of the high temperature product (BNBDA-A) are shown below.
^1H -NMR (600MHz, DMSO) δ=1.00 (dd, 2H), 1.21 (dd, 2H), 1.43 (dt, 2H), 1.61-1.70 (m, 2H), 1.72-1. 85 (m, 2H), 2.50-2.53 (m, 2H), 2.55-2.60 (m, 2H), 3.11 (d, 2H), 3.30 (d, 2H)
^13C -NMR (600MHz, DMSO) δ=27.9, 34.8, 38.7, 39.7, 46.2, 47.4, 48.8, 172.2, 173.2.

(Comparative Example 1)
Using a method similar to that used in Comparative Example 2 of WO 2018/147373, a compound containing 100 mol% of BNBDA-B (stereoisomer B consisting of a compound having an endo/exo type stereostructure represented by the above general formula (30) and a compound having an exo/endo type stereostructure that is its mirror image) (BNBDA consisting only of stereoisomer B) was prepared.

(Comparative Example 2)
Using a method similar to that used in Example 2 of WO 2018/147373, a compound containing 100 mol% of stereoisomer C (hereinafter sometimes referred to as "BNBDA-C") having an endo/endo type stereostructure represented by the following general formula (31) was prepared (BNBDA consisting only of stereoisomer C).

<4> Synthesis of Polyimide Before describing the synthesis method of polyimide employed in each example, the abbreviations of the diamine compounds used in the synthesis of polyimide are shown below. Note that each compound used is a commercially available product.

BAPP: 2,2-bis[4-(4-aminophenoxy)phenyl]propane (manufactured by Seika Corporation)
ODA: 4,4'-diaminodiphenyl ether (manufactured by Seika Corporation)
BPTP: Bis(4-aminophenyl)terephthalate (manufactured by Seika Corporation)
DABAN: 4,4'-diaminobenzanilide (manufactured by Seika Corporation)
PPD: p-phenylenediamine (manufactured by Seika Corporation)
TFMB: 2,2'-bis(trifluoromethyl)benzidine (manufactured by Seika Corporation).

Example 3
<Preparation process of polyamic acid>
First, the low-temperature product obtained in Example 2 (a mixture containing BNBDA-A and BNBDA-B in a molar ratio of 1/10 based on the molar ratio (BNBDA-A/BNBDA-B)) and the high-temperature product (a compound containing 100 mol% BNBDA-A) were mixed together so that the molar ratio of BNBDA-A to BNBDA-B (BNBDA-A/BNBDA-B) was 3/7, thereby preparing 1.65 g (5.00 mmol) of tetracarboxylic anhydride in which the molar ratio of BNBDA-A to BNBDA-B was 3/7.

Next, in a nitrogen atmosphere, BAPP (2.05 g, 5.00 mmol) was introduced as a diamine compound into a 20 mL screw tube, along with tetracarboxylic anhydride (1.65 g, 5.00 mmol) with a molar ratio of BNBDA-A to BNBDA-B of 3/7. Next, 14.8 g of N-methyl-2-pyrrolidone (NMP) was added to the screw tube to obtain a mixed solution. Next, the resulting mixed solution was stirred for 3.5 hours at room temperature (25°C) under a nitrogen atmosphere to produce polyamic acid (PAA), and a reaction solution containing the polyamic acid (PAA solution: PAA varnish) was obtained. A portion of the reaction liquid (solvent: NMP) obtained in this manner was used to remove the solvent and isolate the polyamic acid, after which the polyamic acid was dissolved in N,N-dimethylacetamide to a concentration of 0.5 g/dL to prepare a measurement sample (solution). The intrinsic viscosity [η] of the polyamic acid was measured as described above, and the intrinsic viscosity [η] was found to be 0.65 dL/g.

<Preparation process of polyimide film (thermal imidization process)>
The reaction liquid (PAA varnish) obtained by the preparation step of the polyamic acid was spin-coated on a glass plate consisting of a large slide glass (manufactured by Matsunami Glass Industry Co., Ltd., product name "S9213", length: 76 mm, width: 52 mm, thickness: 1.3 mm) to form a coating film. Thereafter, the glass plate on which the coating film was formed was placed in an oven, and the temperature condition was set to 60°C and left to stand for 4 hours under a nitrogen atmosphere, and then the temperature condition was changed to 300°C (final film formation temperature) and left to stand for 1 hour at 300°C to harden the coating film, thereby obtaining a polyimide-coated glass in which a thin film (film made of polyimide) made of polyimide was coated on the glass plate.

Next, the polyimide-coated glass thus obtained was removed from the oven and immersed in hot water at 90°C for 0.5 hours, and the film was peeled off from the glass plate and collected to obtain a polyimide film having a thickness of 6 μm. The color of the polyimide film thus obtained was confirmed to be colorless and transparent when visually inspected. The IR spectrum of the film thus obtained was measured, and it was confirmed that the C=O stretching vibration of imide carbonyl was observed at 1705 cm ^-1 and 1775 cm ^-1 , confirming that the film thus obtained was made of polyimide.

(Examples 4 to 8 and Comparative Examples 3 to 5)
The types (ratio, etc.) of isomers in the tetracarboxylic anhydride, the amount of tetracarboxylic anhydride used, the type and amount of diamine compound used, the type and amount of solvent used, and the final film-forming temperature in the polyimide preparation process were changed as shown in Table 1, but the same procedure as in Example 3 was used to obtain films made of polyimide. In addition, when the IR spectra of the films obtained in Examples 4 to 8 and Comparative Examples 3 to 5 were measured, the absorption peak of the C=O stretching vibration of imide carbonyl was confirmed in the IR spectrum of each film, and it was confirmed that each of the obtained films was made of polyimide. In addition, with regard to the tetracarboxylic anhydride, in Examples 4 to 8, the high-temperature side product obtained in Example 2 (a compound containing 100 mol% of BNBDA-A) was used alone, in Comparative Example 3, the compound containing 100 mol% of BNBDA-B obtained in Comparative Example 1 was used alone, and in Comparative Examples 4 to 5, the compound containing 100 mol% of BNBDA-C obtained in Comparative Example 2 was used alone. Furthermore, in Examples 7 and 8, a mixture of two types of diamine compounds shown in Table 1 was used. The solvent "DMAc" shown in Table 1 indicates N,N-dimethylacetamide. Furthermore, in Examples 4 to 8 and Comparative Examples 3 to 5, the intrinsic viscosity [η] of the polyamic acids obtained in the polyamic acid preparation step was measured in the same manner as in Example 3. The measurement results are shown in Table 1.

(Example 9)
<Polyimide varnish preparation process>
First, the low-temperature side product and the high-temperature side product obtained in Example 2 were mixed so that the molar ratio of BNBDA-A to BNBDA-B (BNBDA-A/BNBDA-B) was 3/7 to prepare 1.65 g (5.00 mmol) of tetracarboxylic acid anhydride having a molar ratio of BNBDA-A to BNBDA-B of 3/7.

Next, in a nitrogen atmosphere, TFMB (1.60 g, 5.00 mmol) as a diamine compound and tetracarboxylic anhydride (1.65 g, 5.00 mmol) with a molar ratio of BNBDA-A to BNBDA-B of 3/7 were introduced into a 50 mL flask. Next, DMAc (6.5 g) as a solvent, γ-butyrolactone (6.5 g) as a solvent, and triethylamine (25.3 mg) as a reaction accelerator were added to the flask to obtain a mixed solution. Next, the resulting mixed solution was stirred at 180°C for 6 hours under a nitrogen atmosphere to generate polyimide, and a reaction solution containing polyimide (polyimide varnish: PI varnish) was obtained. The intrinsic viscosity [η] of the polyimide was measured in the same manner as the intrinsic viscosity [η] of the polyamic acid described above, except that a measurement sample (solution) with a PI concentration in DMAc of 0.5 g/dL was prepared using a portion of the PI varnish obtained in this manner. The intrinsic viscosity [η] of the polyimide was measured in the same manner as the measurement method for the intrinsic viscosity [η] of the polyamic acid described above, and the result was that the intrinsic viscosity [η] of the polyimide was 0.42 dL/g. Here, the solvent "GBL" in Table 1 stands for gamma-butyrolactone.

<Polyimide film preparation process>
Next, the PI varnish was spin-coated on a glass plate made of a large slide glass (manufactured by Matsunami Glass Industry Co., Ltd., product name "S9213", length: 76 mm, width: 52 mm, thickness: 1.3 mm) to form a coating film of the PI varnish. Thereafter, the glass plate on which the coating film was formed was placed in an oven, and the temperature condition was set to 60 ° C. and left to stand for 4 hours under a nitrogen atmosphere, and then the temperature condition was changed to 350 ° C. (final film formation temperature) and left to stand at 350 ° C. for 1 hour to harden the coating film, thereby obtaining a polyimide-coated glass in which a thin film made of polyimide (a film made of polyimide) was coated on the glass plate. Next, the polyimide-coated glass thus obtained was removed from the oven and immersed in hot water at 90 ° C. for 0.5 hours, and the film was peeled off and collected from the glass plate to obtain a film made of polyimide with a film thickness of 20 μm. The color of the obtained polyimide film was visually confirmed to be colorless and transparent. When the IR spectrum of the film thus obtained was measured, an absorption peak due to the C=O stretching vibration of imide carbonyl was confirmed in the IR spectrum, and it was confirmed that the film obtained was made of polyimide.

[Evaluation of the properties of the polyimides obtained in Examples 3 to 9 and Comparative Examples 3 to 5]
<Measurement of 5% weight loss temperature (Td5%)>
The 5% weight loss temperature of the polyimide obtained in each Example was determined by using the polyimide film produced in each Example and using a thermogravimetric analyzer ("TG/DTA220" manufactured by SII NanoTechnology Inc.) to raise the temperature from room temperature to 40° C. while flowing nitrogen gas, and then heating at a temperature increase rate of 10° C./min from 40° C. as the starting temperature for measurement, and measuring the temperature at which the weight of the sample used decreased by 5%. The results are shown in Table 1.

<Measurement of Yellowness Index (YI)>
The yellowness index (YI) of the polyimide obtained in each Example was determined by using the polyimide film obtained in each Example as it was as a measurement sample and performing measurement in accordance with ASTM E313-05 (issued in 2005) using a spectrophotometer SD6000 (trade name) manufactured by Nippon Denshoku Industries Co., Ltd. The results obtained are shown in Table 1.

<Measurement of coefficient of linear expansion (CTE) and glass transition temperature (Tg)>
The coefficient of linear expansion (CTE) and glass transition temperature (Tg) were determined from the TMA curve obtained by forming a film of 20 mm length and 5 mm width from the polyimide film obtained in each Example (the thickness of the film does not affect the measured value, so the thickness of the film obtained in each Example was used as it is) into a measurement sample and measuring it using a thermomechanical analyzer (Rigaku Corporation, product name "TMA8310") under conditions of a nitrogen atmosphere, tension mode (49 mN), and a temperature rise rate of 5°C/min. The Tg of the polyimide obtained in each Example was determined by measuring the temperature at the intersection of the tangents drawn from the TMA curve to the curve before and after the inflection point. The CTE of the polyimide obtained in each Example was determined by calculating the average value of the change in length per 1°C in the temperature range of 100°C to 200°C from the TMA curve. The results are shown in Table 1.

As is clear from the results shown in Table 1, when comparing Examples 3 to 4 and Comparative Examples 3 to 4 in which BAPP was used as the diamine compound, it was found that when a tetracarboxylic dianhydride containing 30 mol% or more of BNBDA-A relative to the total amount of BNBDA-A and BNBDA-B was used (Examples 3 to 4), the intrinsic viscosity of the polyamic acid (PAA) was higher than that of a tetracarboxylic dianhydride containing 100 mol% BNBDA-B (Comparative Example 3) and a tetracarboxylic dianhydride containing 100 mol% BNBDA-C (Comparative Example 4). Considering that the same conditions were used in Examples 3 to 4 and Comparative Examples 3 to 4 except for the type of tetracarboxylic dianhydride, when a tetracarboxylic dianhydride containing 30 mol% or more of BNBDA-A relative to the total amount of BNBDA-A and BNBDA-B was used as a monomer for polyimide production (Examples 3 to 4), it was found that the monomer exhibited higher polymerization reactivity compared to when a tetracarboxylic dianhydride containing 100 mol% of BNBDA-B was used as a monomer for polyimide production (Comparative Example 3) and when a tetracarboxylic dianhydride containing 100 mol% of BNBDA-C was used as a monomer for polyimide production (Comparative Example 4).

In addition, comparing Example 5 and Comparative Example 5, in which ODA was used as the diamine compound, it was found that when a tetracarboxylic dianhydride containing 100 mol% of BNBDA-A was used (Example 5), the intrinsic viscosity of the polyamic acid (PAA) was higher than that of a tetracarboxylic dianhydride containing 100 mol% of BNBDA-C (Comparative Example 5). From these results, it was found that when a tetracarboxylic dianhydride containing 100 mol% of BNBDA-A was used as a monomer for producing polyimide (Example 5), the monomer exhibited higher polymerization reactivity than when a tetracarboxylic dianhydride containing 100 mol% of BNBDA-C was used as a monomer for producing polyimide (Comparative Example 5).

Thus, when a tetracarboxylic dianhydride containing 30 mol % or more of BNBDA-A relative to the total amount of BNBDA-A and BNBDA-B is used as a monomer for producing polyimide, the reason why the intrinsic viscosity of the polyamic acid (PAA) becomes higher is not necessarily clear. However, the inventors speculate that due to the structure of BNBDA-A, etc., the solubility of the monomer is improved and the polymerization is improved, which results in a higher molecular weight of the resulting polyamic acid, making it possible to form a polyamic acid with a higher intrinsic viscosity.

In addition, when comparing Examples 3 to 4 and Comparative Examples 3 to 4 in which BAPP was used as the diamine compound, the polyimides obtained in Examples 3 to 4 had higher Td5% values, and it was confirmed that in a system in which the diamine compound is the same, by using a tetracarboxylic dianhydride containing 30 mol% or more of BNBDA-A relative to the total amount of BNBDA-A and BNBDA-B, the heat resistance of the polyimide obtained based on Td5% is higher. In addition, when comparing Example 5 and Comparative Example 5, the polyimide obtained in Example 5 had a higher Td5% value, and it was also confirmed that in a system in which the diamine compound is the same, by using a tetracarboxylic dianhydride containing 100 mol% of BNBDA-A, the heat resistance of the polyimide obtained based on Td5% is higher. From the results shown in Table 1, the polyimides obtained in Examples 3 to 9 all had higher Td5% values compared to the polyimides obtained in Comparative Examples 3 to 5. From these results, it can be seen that by using a tetracarboxylic dianhydride containing 30 mol% or more of BNBDA-A relative to the total amount of BNBDA-A and BNBDA-B, a polyimide exhibiting a higher level of heat resistance can be obtained. From these Td5% measurement results, it can be seen that when a tetracarboxylic dianhydride containing 30 mol% or more of BNBDA-A relative to the total amount of BNBDA-A and BNBDA-B is used (Examples 3 to 9), a polyimide with a higher level of heat resistance can be obtained.

Thus, when a tetracarboxylic dianhydride containing 30 mol % or more of BNBDA-A relative to the total amount of BNBDA-A and BNBDA-B is used as a monomer for producing polyimide, the reason for the improved heat resistance of the resulting polyimide is not necessarily clear, but the inventors speculate that the molecular skeleton of the polyimide becomes more linear and rigid due to the structure of BNBDA-A in the tetracarboxylic dianhydride, and that a certain amount or more of such rigid molecular skeleton portions are contained, resulting in higher heat resistance based on Td5%.

As shown in Table 1, all of the polyimides of the present invention have a Tg of 333°C or higher, and from this viewpoint, they are also found to have high heat resistance. In addition, all of the polyimides of the present invention have a CTE of 60 ppm/K or less, and are also found to have excellent dimensional stability.

As described above, according to the present invention, it is possible to provide a tetracarboxylic dianhydride that can be used as a raw monomer for producing polyimides having a higher level of heat resistance and that can further improve polymerization reactivity when used as a raw monomer for producing polyimides, a carbonyl compound that can be used to efficiently produce the tetracarboxylic dianhydride, a polyimide that can have a higher level of heat resistance, and a polyimide precursor resin that can be suitably used to produce the polyimide. The polyimide of the present invention is useful as a material for producing polyimide products for use in the various applications described above (e.g., films for flexible wiring boards, etc.).

Claims (4)

The following general formula (1):
In formula (1), R ¹ each independently represents one selected from the group consisting of a hydrogen atom and a methyl group ;
^R2 and ^R3 each independently represent one selected from the group consisting of a hydrogen atom and a methyl group .
or a tetracarboxylic acid dianhydride comprising an acid dianhydride (A) having an exo/exo stereostructure represented by the following general formula (2):
[In formula (2), R ¹ , R ² and R ³ are the same as R ¹ , R ² and R ³ in formula (1), respectively.]
and a compound having an exo/endo stereostructure which is an enantiomer thereof, and
A tetracarboxylic dianhydride, characterized in that the content of the acid dianhydride (A) relative to the total amount of the acid dianhydrides (A) and (B) is 30 to 100 mol % in terms of molar ratio. The following general formula (3):
In formula (3), R ¹ each independently represents one selected from the group consisting of a hydrogen atom and a methyl group ;
^R2 and ^R3 each independently represent one selected from the group consisting of a hydrogen atom and a methyl group ;
Each R ⁴ independently represents one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, and an aralkyl group having 7 to 20 carbon atoms.
or a carbonyl compound comprising the carbonyl compound (A) having an exo/exo stereostructure represented by the following general formula (4):
[In formula (4), R ¹ , R ² , R ³ and R ⁴ are the same as R ¹ , R ² , R ³ and R ⁴ in formula (3) above, respectively.]
and a compound having an exo/endo stereostructure which is an enantiomer thereof, and
A carbonyl compound, characterized in that the content of the carbonyl compound (A) relative to the total amount of the carbonyl compounds (A) and (B) is 30 to 100 mol % in terms of molar ratio. The following general formula (5):
In formula (5), R ¹ each independently represents one selected from the group consisting of a hydrogen atom and a methyl group ;
^R2 and ^R3 each independently represent one selected from the group consisting of a hydrogen atom and a methyl group ;
R ⁵ represents an arylene group having 6 to 50 carbon atoms.
or a polyimide containing a repeating unit (A) having an exo/exo type stereostructure represented by the following general formula (6):
[In formula (6), R ¹ , R ² , R ³ and R ⁵ are the same as R ¹ , R ² , R ³ and R ⁵ in formula (5), respectively.]
and a structural unit having an exo/endo type stereostructure which is a mirror image thereof, and at least one repeating unit (B) selected from the group consisting of a structural unit having an endo/exo type stereostructure represented by the formula :
A polyimide characterized in that the content of the repeating unit (A) relative to the total amount of the repeating units (A) and (B) is 30 to 100 mol % in terms of molar ratio. The following general formula (7):
In formula (7), R ¹ each independently represents one selected from the group consisting of a hydrogen atom and a methyl group ;
^R2 and ^R3 each independently represent one selected from the group consisting of a hydrogen atom and a methyl group ;
^R5 represents an arylene group having 6 to 50 carbon atoms;
Each Y ¹ independently represents one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, and an alkylsilyl group having 3 to 9 carbon atoms;
One of the bonds represented by *1 and *2 is bonded to the carbon atom a forming the norbornane ring, the other of the bonds represented by *1 and *2 is bonded to the carbon atom b forming the norbornane ring, one of the bonds represented by *3 and *4 is bonded to the carbon atom c forming the norbornane ring, and the other of the bonds represented by *3 and *4 is bonded to the carbon atom d forming the norbornane ring.]
or a polyimide precursor resin containing a repeating unit ( A') having an exo/exo type stereostructure represented by the following general formula (8):
[In formula (8), R ¹ , R ² , R ³ , R ⁵ , Y ¹ , a to d, and *1 to *4 are respectively defined as R ¹ , R ² , R ³ , R ⁵ , Y ¹ , a to d, and *1 to *4 in formula (7) above.]
and a structural unit having an exo/endo type stereostructure which is a mirror image thereof, and at least one repeating unit (B') selected from the group consisting of a structural unit having an endo/exo type stereostructure represented by the formula :
A polyimide precursor resin, characterized in that the content of the repeating unit (A') relative to the total amount of the repeating units (A') and (B') is 30 to 100 mol % in terms of molar ratio.